Researches on malaria Nobel Lecture, December, 12, 1902

oars to the boat.

In the spotted-winged mosquitoes which I now found at Secunderabad I

noticed at once the general difference of shape, the peculiar attitude of the in-

sects when at rest, the marks on the wings, and the appearance of the eggs (as

seen within the body of the female when dissected); but the larvae could not

be studied until later.* The adults were very delicate, pale-brown creatures,

which by common consent seemed scarcely to bite man, though they were

* It was principally my assistant, Mahomed Bux, who ascertained, as a general rule, the

attitude of the larvae.

56

    1 9 0 2   R . R O SS

numerous enough to have caused much irritation had they done so. They

swarmed in my own quarters, but seldom bit me. They abounded also in the

houses of the other officers of the regiment, who, with their families had re-

mained quite free from malarial fever. Consequently I was not disposed to

think that they had anything to do with the disease. On the other hand the

grey mosquitoes swarmed in the barracks, but were much less numerous in

the officer’s quarters (situated some hundreds of yards to leeward of the bar-

racks). Suspicion therefore first attached to the latter variety.

I determined, however, not to be swayed by such considerations, but to

make a most complete and exhaustive test of all the varieties which I could

procure - even at the cost of repeating much of my old negative work, during

which, laborious as it was, I may have overlooked the object I was in search of.

A number of natives were employed to collect larvae from far and wide round

the barracks. These larvae were kept in separate bottles, and when the adult

insects appeared they were released within mosquito nets in which the patients

were placed. The insects were applied sometimes during the day in a darkened

room; and were sometimes fed all night. After feeding, the gorged insects

were collected in small bottles containing a little water and were kept for

several days before being dissected. The procedure was therefore the same as

before; but now, in order to ensure at least definite negative results, redoubled

care was taken; almost every cell was examined; even the integument and legs

were not neglected; the evacuations of the insects found in the bottles, and the

contents of the intestine were scrupulously searched; at the end of the first

examination staining reagents were often run through the preparation, and it

was searched again with care. The work, which was continued from 8 a.m.

to 3 or 4 p.m. with a short interval for breakfast, was most exhausting, and so

blinding that I could scarcely see afterwards; and the difficulty was increased

by the fact that my microscope was almost worn out, the screws being rusted

with sweat from my hands and forehead, and my only remaining eye-piece

being cracked, while swarms of flies persecuted me at their pleasure as I sat

with both hands engaged at the instrument. As the year had almost been rain-

less (it was the first year of plague and famine) the heat was almost intolerable,

and a punkah could not be used for fear of injuring the delicate dissections.

Fortunately my invaluable oil-immersion object-glass remained good.

Towards the middle of August I had exhaustively searched numerous grey

mosquitoes and a few brindled mosquitoes. The results were absolutely nega-

tive; the insects contained nothing whatever. Then, I think for the first time,

I began to feel that the long quest had been in vain and that a flaw existed some-

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57

where in the induction. The disease was there, the mosquitoes were there -

how was it that I found nothing? I may perhaps be pardoned for dwelling on

my personal feelings during that time, and the astonishing time which fol-

lowed. Science too has its drama; and the actor on that real scene cannot help

being moved when he remembers it - although it may appear trivial enough

to others.

I had remembered the small dappled-winged mosquitoes, but as I could

not succeed either in finding their larvae or in inducing the adult insects to

bite patients, I could make no experiments with them. On the 15th August,

however, one of my assistants brought me a bottle of larvae, many of which

hatched out next day. Among them I found several dappled-winged mos-

quitoes, evidently of the same genus as those found about the barracks, but

much larger and stronger. Delighted with this capture I fed them (and they

proved to be very voracious) on a case with crescents in the blood. Expecting

to find more in the breeding bottle and wishing to watch the escape of the

motile filaments in this new variety, I dissected four of them for this purpose

immediately after feeding. This proved to be most unfortunate, as there were

no more of these insects in the bottle, and the results as regards the motile

filaments were negative. I had, however, four of the gorged dappled-winged

mosquitoes left; but by bad luck two of the dissections were very imperfect

and I found nothing. On the 20th August I had two remaining insects both

living. Both had been fed on the 16th instant. I had much work to do with

other mosquitoes, and was not able to attend to these until late in the afternoon

when my sight had become very fatigued. The seventh dappled-winged mos-

quito was then successfully dissected. Every cell was searched, and to my in-

tense disappointment nothing whatever was found, until I came to the insect’s

stomach. Here, however, just as I was about to abandon the examination, I

saw a very delicate circular cell apparently lying amongst the ordinary cells of

the organ, and scarcely distinguishable from them. Almost instinctively I felt

that here was something new. On looking further, another and another

similar object presented itself. I now focussed the lens carefully on one of these,

and found that it contained a few minute granules of some black substance

exactly like the pigment of the parasite of malaria. I counted altogether twelve

of these cells in the insect, but was so tired with work and had been so often

disappointed before that I did not at the moment recognize the value of the

observation. After mounting the preparation I went home and slept for nearly

an hour. On waking, my first thought was that the problem was solved; and

so it was.

58

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Next morning I returned to the hospital with much apprehension lest the

eighth and last dappled-winged mosquito should have died and become de-

composed during the night. It was alive; and was killed and dissected with

much anxiety. Similar bodies were present in it, only they were distinctly larger.

The seventh mosquito had been dissected four days after finding; the eighth

five days after feeding; the parasites in the latter had lived a day longer than

those in the former and were consequently larger. Both insects had been bred

from larvae in captivity; both had been fed for the first time on the same

person - a case of malaria; no such objects as these pigmented cells - as I then

called them - had ever before been seen in the hundreds of mosquitoes exam-

ined by me; the objects lay, not in the stomach cavity of the insects, but in the

thickness of the stomach wall; all contained a number of black granules pre-

cisely similar in appearance to those contained by the parasites of malaria, and

quite unlike anything which I had ever seen in any mosquito previously.

Lastly, these two mosquitoes were the first of the kind which I had ever tested.*

The mind long engaged with a single problem often acquires a kind of

prophetic insight, apparently stronger than reason, which tells the truth,

though the actual arguments may look feeble enough when put upon paper.

Such an insight is mainly based, I suppose, on a concentration of small proba-

bilities each of which may have little weight of itself; but in this case at all

events the insight was there and spoke the truth.

These two observations solved the malaria problem. They did not complete

the story, certainly; but they furnished the clue. At a stroke they gave both of

the two unknown quantities - the kind of mosquito implicated and the posi-

tion and appearance of the parasites within it. The great difficulty was really

overcome; and all the multitude of important results which have since been

obtained were obtained solely by the easy task of following this clue - a work

for children. We may rest assured that if these observations had not been made

we should still have remained ignorant of the mode in which this important

disease, with its annual death roll of millions, is propagated - aye, and would

have remained ignorant of it until some one else had taken up the same in-

vestigation by the same method.

And no other method would have solved the problem. It was necessary to

* On the assumption that these cells had developed from the motile filaments it was dif-

ficult at the moment to explain the pigment within them - as the motile filaments have no

pigment. I thought it possible, however, that after fixing themselves in the stomach wall

they might be able to derive haemoglobin from the contents of the organ, and afterwards

convert this into the pigment.

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59

find not one but two unknown quantities, and neither could be found by it-

self. There are no phenomena which would serve to indicate the kind of mos-

quito. In nearly all malarious places there are many kinds of mosquitoes, and,

as in the Sigur Ghat and other places, the malaria-bearing species are in no

way predominant among them either in numbers or in any other way. Indeed

the malaria-bearing species occur in places where malaria has not been known

in the memory of man, as around Liverpool. By what process of reasoning

then could we isolate the species? It might possibly have been practicable to

detect it by a very long series of experiments aimed at infecting men by the

bites of successive species of mosquitoes; but no one would have undertaken

such a work without the guide of a very strong theory in favour of inoculation

by the bite; and the theory of King and Bignami to this effect was little more

than a conjecture. It was not likely that the first species tried would have given

successful results, as my own experiments of 1896 showed. Even if, after a

multitude of costly and dangerous experiments, a positive result had been at-

tained by this method, it would always be open to doubt (seeing that the

experiments would have to be done in a malarious country) whether the case

was not merely one of relapse; and another long series of experiments would

be required to eliminate this doubt. And then, even when the proper species

of mosquito was detected, there would still be no guide to the form and posi-

tion of the parasites within it, or even to the way in which they enter the insect

(Bignami thought that they enter the larvae from marsh water). No, the thing

was not practical. Bignami himself abandoned his experiments on his own

theory after the first failure

29

and did not resume them until after my work

had clearly indicated both the kind o  mosquito implicated and the route of

f

infection. The only practicable method was to attempt to find both unknown

quantities simultaneously by the "trial and failure system" - such as I adopted.*

The discovery of the pigmented cells, therefore, ended for me at least the

old research, the period of doubt, the groping in the dark. The secret spring

had been touched, the door flew open, the path led onward full in the light,

and it was obvious that science and humanity had found a new dominion.

But it was necessary to follow the clue forthwith; to watch the development

of the pigmented cells in mosquito after mosquito; to ascertain what became

of them; to fathom the mystery of the route of infection; and then to save

human life in the gross, perhaps to open continents to civilization.

* I mention these facts because many writers on the subject seem to think that the original

discovery was made merely by catching the first mosquito and finding the pigmented

cells within it.

60

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The first thing was to obtain more - hundreds - of these large dappled-

winged mosquitoes. Alas, the man who had found them had, contrary to my

orders, put the larvae from many sources in the same bottle! All the larvae

from all these sources were collected - but no more dappled-winged mos-

quitoes! I turned then to the small but similar variety which swarmed about

the barracks. Being evidently of the same genus, they too would probably

harbour the parasites; but though my men and myself searched high and low

for their larvae, we could not find them. I could scarcely even persuade the

adults to lay their eggs in captivity.

Thinking that in spite of all my care I may have overlooked the pigmented

cells in the grey and brindled mosquitoes, I now searched for them in the

stomachs of a number of these, but without result. A number of the small

dappled-winged mosquitoes caught about the hospital were also examined

for them in vain. These observations served however for a "control" on the

two positive cases.

Owing to the great heat at Secunderabad I had been obliged to leave my

family at Ootacamund, and was now compelled to go to Bangalore for a few

days in order to settle them there for the remainder of the summer. This gave

me leisure for writing a report to the government of India on the discovery of

the pigmented cells, and also a short paper on the same subject for publication.

The latter was of course intended only as a preliminary to a detailed report

which I hoped to be able to publish in a few months and which I thought

Fig.2. Pigmented cells (zygotes) of aestivo-autumnal parasite in dappled-winged mos-

quitoes (Anopheles). From  Ross’s paper, British Medical Journal, 18th Dec. 1897, p. 1787.

    R E S E A R C H E S   O N   M A L A R I A

61

would contain the full explication of the whole problem. I described my

method in a few opening lines, being careful to note that the mosquitoes used

by me had been "bred in bottles from the larva". The mosquitoes were then

described as well as possible - the spots on the wings and the peculiar shape of

the eggs being noted, but reference to the peculiar attitude being inadvertently

omitted. Next I gave in detail the circumstances under which the pigmented

cells were found, together with a description of them; and finally discussed,

very guardedly, their probable relation to the parasite of malaria. I had

brought the original preparations with me, and now showed them to my

friend Surgeon Major John Smyth, who at my request kindly added a note to

my paper, corroborating my description. They were then despatched by post

to Manson. My paper, however, did not appear until December

38

; but when

it did so it was accompanied by an excellent drawing of the pigmented cells

furnished at the instance of Manson, and also by remarks of Manson, Bland

Sutton, and Thin, who discussed the new objects - the last holding that the

cells were ordinary cells of the stomach wall into which malarial pigment had

entered in some manner from the stomach cavity. This preliminary article

was published by me for the express purpose of guiding the researches of

others; and in fact anyone who had read my description of the pigmented cells

and of the dappled-winged mosquitoes would now have had little difficulty

in repeating my work.*

On my return to Secunderabad I was much disappointed to find that the

larvae of neither the large nor the small species of dappled-winged mosquito

had yet been collected. Consequently in the intervals of searching for them,

I spent my time in examining the stomachs of all the mosquitoes I could catch

for the pigmented cells. I hoped especially to find them in the small dappled-

winged insects caught about the hospital, where there were several cases of

malaria, but was disappointed. On the 18th September, however, a large grey

mosquito was observed feeding on a patient suffering from the benign tertian

parasites and was promptly secured. The stomach was full of black blood, so

that it must have fed previously (freshly imbibed blood showing red in the

insects) as well as on this occasion. It was kept until the 21st and was then

dissected. To my delight the pigmented cells were again found, in consider-

able numbers; but they were larger even than those of the mosquito of the

21st August. As this particular insect had not been bred from the larva in cap-

tivity I could not say for certain where it had become infected, but I thought

* This is exactly what was done by the Italian observers fifteen months later (see sec-

tion 23).

62

    1 9 0 2   R . R O SS

it likely that it had been feeding on the case of tertian all the time (that is, from

about a week before it was killed) as the patient was in a bed by himself in a

corner of a large nearly empty ward. Hence I naturally inferred as a probabil-

ity that the pigmented cells in this insect were derived from that case; and I

thought that their large size suggested that they must have been so derived

about a week before the insect was killed. But of course I could not speak

with absolute assurance on these points.*

Meanwhile swarms of small grey larvae had been found in an isolated pool

of rain-water, which I had overlooked because it was on the top of a hillock

where pools were not likely to exist. On hatching out, these were found to be

the long-sought larvae of the small dappled-winged mosquitoes. I observed

at once that they had no breathing tubes and that their attitude was peculiar as

compared with the larvae of other mosquitoes; and noticed also that the pool

in which they were found seemed too shallow and evanescent for the latter -

facts shown by me and my colleagues in 1899 to be of the greatest importance

in connection with the prevention of malaria. Directly enough of the adults

appeared from the larvae in the breeding-bottle, they were released in large

numbers within the mosquito-net of a patient with crescents in his blood.

Next morning only two of them were found to have fed themselves. One

was killed next day, but nothing was found in it. The second was killed the

day after, and was found to contain a large number of very small pigmented

cells! This really almost clinched the matter; for three out of four dappled-

winged mosquitoes bred from the larvae in captivity and fed on cases of cres-

cents had been found to contain pigmented cells; while these cells could not

be seen in insects of the same kind which had not been so fed. Just at this time

I wrote to Manson, in a state of unbounded delight, that he might expect to

know the full life-history of the parasites of malaria in the mosquito within a

few weeks.

Next day however, I received telegraphic instruction from Government

ordering me to proceed forthwith to Kherwara in Rajputana - a place a thou-

sand miles distant !

14. Interruption (September 1897-February 1898). It would be difficult for others

to understand the effect of this cruel blow. Here in Secunderabad I had numer-

ous cases of malaria in my own hospital, and, moreover, the men had been

trained to submit to mosquito bites - a matter often of some difficulty with

* This mosquito also contained a number of the swarm-spores which I had observed in

the Sigur Ghat.

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63

the superstitious natives of India. I had also experienced assistants hired by

myself for the work; and, above all, the proper kind of mosquitoes, including

their larvae, just found in abundance. There is no doubt whatever that, had I

been left at Secunderabad, I could easily have traced the whole life-history of

the human parasites in dappled-winged mosquitoes within a few weeks. But

at Kherwara I did not know what would happen. It was in the north; winter

was approaching; and I knew that mosquitoes would refuse to bite in the cold.

I failed even to guess the reason for this sudden transfer. The astonishing dis-

covery of the pigmented cells had been officially and fully reported to the

Government through the chiefs of my own department; malaria is the most

important disease of India; and I thought that my superiors were taking the

greatest possible interest in researches which touched so vital a subject - I

thought that they would make every effort to leave me undisturbed, if not to

give me active help.

But the orders were peremptory and not to be discussed. Within two days

(26th September) I was on the week’s journey to Kherwara. I saw only one

gleam of comfort. It was impossible that my chiefs, medical men, would con-

sent to interrupt my work at such a moment. There must undoubtedly be a

bad outbreak of malarial fever at Kherwara which would throw great light

on my subject.

When I arrived at the place however - a petty station with three or four

Europeans (whom I shall always remember for their kindness), and part of a

native regiment of Bhils, isolated in the midst of miles of wild country far

removed from civilization - I was told that there was no malaria there; there

had not been a case for months !

This then was my Elba - almost my île du Diable; and I saw no prospect of

escaping from it for a year at least. After excusing myself from accepting the

appointment in Berar, I had indeed later asked to be remembered for a per-

manent appointment to which I thought my long service (more than sixteen

years) and my work at Bangalore had at least given me some claim. But this

was only a temporary and insignificant one, generally held by juniors; and I

do not know why the transfer was made, unless possibly (though not certain-

ly) for reasons connected with the Afridi war. At all events it was made with-

out reference to my researches. I wrote officially to my superiors, begging to

be allowed to return to Secunderabad to continue my work; but received

only a reprimand in consequence. There was no escape; but my pension was

due to me the following April, and I made up my mind to apply for it as soon

as the war was over, and to continue my researches as a private person.

64

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The cold weather came on apace, and at first it appeared to be utterly im-

possible to work. There were no cases of malaria and scarcely any mosquitoes.

Much to my pleasure, however, I found a few dappled-winged gnats, and

observed again that their larvae lived in water on the ground - namely in a pit

and an old well - apparently almost as dormant as the adults were. I kept a

single one alive in a bottle for two months without its developing.

Shortly after arrival at Kherwara I wrote down a brief account of the find-

ing of the pigmented cells in the third and fourth mosquitoes. At the end of

January the British Medical J

 

ournal containing my previous paper on the

cells

38

, together with remarks by Manson, Bland Sutton, and Thin, reached

me. I therefore rewrote the beginning of my second paper; and added a refer-

ence to some work which I had been able to do with pigeons, and also a long

discussion of Thin’s remarks, in which I showed that his position with regard

to the pigmented cells was untenable. The paper was published in February.

I did not explicitly say that the third dappled-winged mosquito had been bred

from the larva in captivity, because it was evident that this fact would be in-

ferred from the opening of the first paper of which the second was obviously

a continuation. But I said that the grey mosquito in which pigmented cells

had been found was "observed feeding on a patient", and that "I judged for

many reasons that it had been feeding occasionally on the same man for several

days" showing clearly enough that this insect had not been bred from the

larva in captivity. The facts might have been put more explicitly at the time;

but they are apparent enough to any candid reader.* In the paper the order of

the third and fourth mosquitoes is changed for purposes of description - the

case of the grey mosquito being put last because it was doubtful.

The work with pigeons just referred to was as follows. Being unable to ob-

tain cases of human malaria I turned to the malaria of birds which had long

been known to harbour parasites closely similar in appearance and life-history

to the malaria parasites of man. Both Manson and I had long recognized the

technical advantages of working with these organisms. I immediately found

the parasites of Labbé’s genus Halteridium in the pigeons of Kherwara; but

could not induce mosquitoes to bite the birds. Observing, however, that they

were infested by a species of blood-sucking fly, I examined thirty of these, and

* When I

 

wrote these papers I did not suspect that every line of mine, even in some of

my private letters, would be subjected to a minute and unscrupulous analysis in the hope

of finding discrepancies which would serve to discredit my observations. Every possible

artifice has been used for this purpose by the very men who learnt all they knew from

these very publications.

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65

some lice, fed on infected pigeons. No pigmented cells were, however, found

in them.

At last when the weather became warmer in February several cases of quar-

tan fever occurred among the troops, probably relapses. The dappled-winged

mosquitoes still refused to bite; but I succeeded in feeding a number of brin-

dled mosquitoes of a peculiar brown species on the cases. The results were again

negative in thirty-four of these insects.

I was just about to apply for my pension when welcome news arrived. I had

of course given full details of my sudden transfer to Manson; and he had ex-

erted himself to influence the government of India and the Director General

of the Indian Medical Service (then Surgeon General Cleghorn) to put me on

special duty to continue my researches. I had urged the same thing upon the

Director General; but, unfortunately as it happened, suggested that one good

place for the work would be Assam, where an epidemic of kala-azar - a disease

which Rogers had recently reported to be malaria - had long been raging.

However, I now received a telegram stating that I had been placed on special

duty to investigate malaria and kala-azar in Calcutta and Assam for six

months.* My five months’ imprisonment was at an end. I arrived in Calcutta

on the 17th February 1898; and was joined there by my family, with all my

books and notes which had been with them at Bangalore all this time.

15. Calcutta (February-April, 1898). The theory proved. 

Now in recompense

for the tribulations of Kherwara, opened a glorious time, during which the

amazing story of malaria was unrolled little by little. The great induction had

given the clue; now, following the clue step by step, we were to be led into

regions where Nature revealed herself wonderful beyond the imagination of

any of us. In the background was something greater still - the possibility of

saving human life on the large scale.

I am happy to be able to begin this part of the narrative with a brief account

of the brilliant and important discovery of MacCallum. It will be remembered

that Manson had thought the motile filaments to be flagellated spores; that I

had studied them much without being able to learn anything new about them

except that they are certainly living organisms; and that when I finally found

the pigmented cells I thought that these were derived from the motile fila-

ments, and had absorbed their melanin from the haemoglobin in the stomach

cavity of the insects. In his letter of the 11th August however, Manson sent

me a paper by Simond, suggesting that the similar motile filaments of certain

* Afterwards extended to one year.

66

   1 9 0 2   R .R OS S

Coccidia 

are not of the nature of flagellated spores at all, but of the nature of

sperms

35

. How were these facts to be reconciled?

In a letter dated the 17th November 1897 Manson informed me that a dis-

covery had been made by W. G. MacCallum in America regarding the motile

filaments, showing independently that they are of the nature suggested by

Simond’s work. He did not send me the literature; and as his letter reached

me at Kherwara I could not then obtain it. Shortly after my arrival at Calcutta

however, I procured a copy of the Lancet

36 

which gave an abstract of Mac-

Callum’s work. The discovery was as follows.

In 1897 MacCallum undertook a study of the motile filaments. Working

with the Halteridium of birds he noticed first that the gametocytes seemed to

be of two kinds, namely one kind which produced the motile filaments, and

another kind which did not do so. On watching two of these cells, one of each

kind in the same field of the microscope, he observed (July 1897) that the fila-

ments escaped from one as usual; that it moved about actively for a time; and

then approaching the other gametocyte actually entered it. Other observa-

tions of MacCallum and Opie, made both on Halteridium and on the cres-

centic gametocytes of the aestivo-autumnal parasite of man, confirmed this

beautiful discovery. The fact, as previously shown by Sacharoff, that the fila-

ments contain chromatin was now explained; and also the facts that they

escape and move about in the blood. They are, indeed, sperms which are emit-

ted from the one kind of gametocytes, the males, and which fertilize the other

kind, the females. Thus these minute parasites, among the lowest of creatures,

have their sexes, and a form of sexual reproduction precisely like that of the

highest animals.

More than this, MacCallum observed in the case of Halteriditim of the crow

that the female cell, motionless before fertilization, afterwards becomes elon-

gated and vigorous, and moves across the field in vitro. This motile form had

apparently long been seen by Danilewski and had been called by him a vermi-

cule.*

So much for the motile filaments, but now what were the pigmented cells?

Everyone seems to have thought that as soon as the flagellate spores disappear-

ed, so did Manson’s theory. But it was not so. The induction remained as

strong as before; the locus of the phenomenon was still in all probability the

* I should certainly have observed these facts when I was making a special study of the

motile filaments in 1895 and 1896. I repeatedly saw them apparently attacking leuco-

cytes

42

. The reason why I found that only a percentage of crescents emit the filaments in

the mosquito’s stomach is now explained the remainder were females (section 11).

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67

stomach-cavity of the mosquito. MacCallum’s work seems to have reached

Manson shortly after my discovery of the pigmented cells came to him. He

connected the two groups of facts in a moment. My pigmented cells were the

vermicules, or fertilized female cells, which had burrowed into the insect’s tissues for the

purpose of undergoing further development there. 

This, and not my hypothesis

made before MacCallum’s paper was known to me, explained the presence of

pigment in the cells. He communicated his views to me in his letter of the 7th

February, and published them later

41

.

Meanwhile, after another struggle, I was again in sight of the pigmented

cells. On my arrival at Calcutta I found myself installed in the convenient little

laboratory which had been formerly used by Professor D. D. Cunningham.

There was a native assistant there; but I hired at my own expense several oth-

ers, especially a most intelligent Mahommedan named Mahommed Bux, who

after he had been trained showed great enthusiasm and gave me much assist-

ance. To my delight I at once noted several varieties of dappled-winged mos-

quitoes, besides many kinds of grey and brindled mosquitoes, actually within

the laboratory, and found the breeding-places of the latter just outside. Those

of the dappled-winged mosquitoes were detected a little later; and were again

seen to be pools of water on the ground. The next thing was to obtain cases of

malaria; but here I was met by an unexpected and most unforeseen misfor-

tune. The plague had been raging all this time in India; and on the Govern-

ment’s trying to introduce Haffkine’s prophylactic inoculation in Calcutta

just before my arrival, serious riots, during which many of the Europeans had

felt themselves obliged to go about armed with revolvers, had occurred. The

ignorant populace, thinking that the British were trying to inoculate them

with and not against plague, flew into paroxysms of terror at the very sight of

a European hakim (physician), while anything remotely resembling inocula-

tion made them frantic. The physicians of the Calcutta hospitals were evident-

ly very unwilling that I should use their cases for my experiments under these

circumstances; and, as I had no hospital of my own as in Secunderabad and

Bangalore, I was forced to send my assistants into the bazaar (native parts of

the city) in order to try to induce patients to come to me on payment. Calcutta

is not very malarious, especially at that time of the year, and it was only on

large payment that several beggars with fever were induced to come to me;

but when I proposed to prick their fingers in order to examine their blood

they generally left their money, took up their crutches, and fled without a

word! This placed me in complete perplexity as to what to do, until I remem-

bered the malaria of birds. A number of crows, pigeons, weaver-birds, spar-

68

    1 9 0 2   R . R O SS

rows, and larks were then immediately procured, and experiments com-

menced on them without delay.

The malarious parasites of birds are exceedingly closely related to those of

men, and together with these and the malaria parasites of bats and monkeys

form a group which is quite distinct from the intracorpuscular protozoa of

some mammalia, such as the Pyrosoma bigeminum of cattle, and of reptiles, such

as Drepanidium. The true malaria parasites (namely the intracorpuscular proto-

zoa of man, birds, bats, and monkeys) are distinguished by their generally

amoeboid character, by their possession of the characteristic black or brown

pigment (melanin), and by an identical life-history as regards the production

and appearance of the spores within the corpuscles, and of the motile filaments

shortly after the blood containing them is drawn from the host. The parasites

of birds differ from those of man only in some very small morphological de-

tails; and are so similar that in the earliest sub-classification of the group by

Grassi, one of the parasites of birds commonly called Proteoroma is placed with

two of the human species, the quartan and tertian, in one genus; while the

other parasite of birds, commonly called Halteridium, is placed in another

genus together with the remaining parasite of man, that of the pernicious,

remittent, or aestivo-autumnal fevers. The latter part of Grassi’s classification

was wrong; and we now recognize that both the parasites of birds must be

placed in one group with the quartan and tertian parasites of man; while the

third human species must be placed in a group by itself, owing to the distinct

shape of its gametocytes (crescents). Thus zoologically, the avian species are

actually more nearly related to two of the human species than these are to the

third human species. Anyone who had actually studied all these parasites,

moreover, would have little doubt that they would be found to possess prac-

tically identical life-histories outside the vertebrate hosts, or at least life-histo-

ries which, if not identical, would be closely similar. It did not of course follow

with certainty that the carrying agents of the avian parasites would be the

same as those of the human species; but we could safely assume that they would

be some kind of blood-sucking arthropod. At all events it was certain that the

discovery of the life-history of the avian parasites would immediately open up

that of the human organisms; while the practical difficulties of working with

birds and infecting them would be less than with men. In fact I should have

been wise to have begun my researches with birds in 1895. I therefore deter-

mined to employ birds at once pending the subsidence of the plague-scare,

when I purposed of course to return to the human parasites; and there is no

doubt that this was the right course.

    R E S E A R C H E S   O N   M A L A R I A

69

It was first advisable to see whether mosquitoes would not carry one or both

of the avian parasites. A number of crows and pigeons had been found to con-

tain Halteridirium; but without waiting to examine the other birds, I placed one

crow, two pigeons, four larks and six sparrows in several cages all within the

same mosquito netting, and then in the evening released within the net a num-

ber of grey and brindled mosquitoes bred from the larva in captivity. Next

morning many of the grey mosquitoes were found gorged and were collected

and kept for several days according to my rules. On the 13th and 14th March

I dissected them one by one. When thirteen had been examined with negative

results I began to fear that I had committed myself to another tedious search

for the proper kind of host of the avian parasites. But fortune was kinder on

this occasion; the fourteenth mosquito had pigmented cells precisely similar

to those which I had found in the dappled-winged mosquitoes fed on patients

with crescents.

Next I examined the larks and sparrows used in this experiment together

with the crows and pigeons, and found that they contained not Halteridium

but Proteosoma; so that it was doubtful from which kind of parasite the pig-

mented cell had been developed. Consequently I now put the birds with Halteri-

dium 

in one net and those with Proteosoma in another, and released within both

nets numbers of grey mosquitoes bred in the same bottle. Of thirty-four of

these fed on the birds with Halteridium all were negative; but out of nine fed

on the birds with Proteosoma, no less than five contained pigmented cells.

This result was obtained on the 20th March and practically proved the mos-

quito theory of malaria. Out of hundreds of grey mosquitoes previously ex-

amined none had contained pigmented cells except one which had been

caught feeding on a case of tertian (section 13), and one which may have bit-

ten one of the birds with Proteosoma in the experiment of the 14th March.

Now, however, no less than five out of nine fed on birds with Proteosoma

contained them. Mathematically therefore the probabilities were enormous

(amounting almost to certainty) in favour of the view that the pigmented

cells in this experiment had been derived from the Proteosoma.

The cells were in the tissues of the insect; the parasite must therefore be

able to make its way into and live in mosquitoes; precisely similar cells had

been found in mosquitoes fed on men with malaria - and the chain of proof

was complete.

But the fact that the pigmented cells in the mosquitoes are indeed derived

from the parasites in the birds was of such fundamental importance that it re-

quired the most formal and rigid proof - especially as no life-history of a pro-

70

  1 9 0 2   R.R OS S

tozoal organism able to transfer itself from one host to another was then

known to science.*

I therefore now commenced a long series of differential experiments in

order to establish the fact thoroughly. Grey mosquitoes bred from the larva in

captivity were fed (a) on birds with Proteosoma and (b) on birds without Pro-

teosoma, 

and the results compared. The details will be found in my Report-Q.

Out of 245 grey mosquitoes fed on birds with Proteosoma, 178, or 72 per cent,

contained pigmented cells, while out of 249 of them fed on blood containing

other parasites or no parasites, not a single one contained them.

Another experiment was the following. Three sparrows were selected, one

with no parasites, one with a few Proteosoma, and one with many Proteosoma.

They were placed in separate nets, and numbers of grey mosquitoes from the

same breeding bottle were fed simultaneously but separately on them. Ten

mosquitoes fed on each bird were then examined, and the total number of

pigmented cells in all of them were counted. The results from a hasty enumer-

ation made by myself were as follows. No pigmented cells were found in the

ten mosquitoes fed on the sparrow without parasites; 292 in the ten mosqui-

toes fed on the sparrow with a few Proteosoma; and 1009 in the ten fed on the

one with many Proteosoma

42

. The preparations were sent to Manson, who

made a more careful enumeration and found 0, 571, and 1084, pigmented cells

in the three sets of mosquitoes separately

41

.

The fact then was proved, and the theory that the parasites of malaria de-

velop in mosquitoes was practically established. Meanwhile I had been pro-

ceeding in the fascinating task of watching the progress of that development.

A number of grey mosquitoes would be fed on an infected bird and would be

dissected two, three, four days, and so on, afterward. It was thus found that the

pigmented cells grew rapidly in size until about the eighth day, when they be-

came so large as to be almost visible to the naked eye. At this point they seemed

to become mature; and it could be seen that many of them burst within the

insect; because mosquitoes which had been infected more than eight or nine

days before dissection were found to contain not the mature pigmented cells,

but only their empty capsules. For the moment I could not ascertain what

became of their contents.

This part of the work led to an interesting observation which influenced all

subsequent researches on mosquito-borne disease. It will be remembered that

Manson had always thought that a few days after her meal of blood the female

* The life-history of Pyrosoma in ticks is not even yet known; and the transference of try-

panosomes by flies appears to be merely mechanical.

    R E S E A R C H E S   O N   M A L A R I A

71

mosquito laid her eggs and died; at this moment he considered both filariae

and malaria parasites escape into the water from the insect

26

. I had accepted

this view, but had frequently observed that the insects do not die immediately

after laying their eggs; and now, as I watched the pigmented cells growing

larger and larger without apparently ripening, even five days after the insect

was fed, it occurred to me that we had been allowing our mosquitoes to die so

early owing to a very simple reason - we had omitted to feed them again! I

therefore fed my infected mosquitoes a second and a third time, and more;

and found that I could easily keep them alive for a month.* This enabled me to

work out the development of the malaria parasites completely; and also help-

ed others subsequently to find a further stage in the development of filariae,

and to ascertain the mode of infection in yellow fever.

I did not succeed, and, indeed, scarcely attempted to find the host of Halteri-

dium. 

Nor was there time to work out the formation and behaviour of the

"vermicules" in the stomach cavity of the mosquito - although this could have

been done very easily; but on one occasion I saw the motile vermicule of

crow’s Halteridium in a brindled mosquito.

Of course all this time anxious efforts had been made to obtain cases of hu-

man malaria for experiment. Early in March I succeeded after much difficulty

in finding an old beggar with a few crescents willing to submit to the dreaded

operations; and I examined 41 grey mosquitoes and 15 dark greenish dappled-

winged mosquitoes which had been fed on him. The first kind were tried

merely as controls, and were of course negative; but, much to my surprise and

disappointment, so were the latter. I attributed the failure to the facts that the

crescents were very scarce in the patient, that the mosquitoes fed very sparing-

ly, and that there was a spell of very cold weather (for Calcutta) at the time.

A few unsatisfactory experiments with grey mosquitoes fed on a child with

mild tertian parasites also failed. In spite of all efforts no other cases could be

procured.

A full list of all these experiments, beginning with my earliest work in 1895,

will be found in my Report written a few weeks later

42

.

Recognizing, of course, the inadequacy of my nomenclature for mosqui-

toes and the urgent necessity for employing the correct entomological names

for the various species used by me, and having failed to obtain any literature

on the subject, I now applied for assistance at the Indian Museum in Calcutta ;

but I

 

received a brief reply to the effect that the savants there could give me no

* I refed them on healthy birds ; but Bancroft subsequently found that they could be kept

alive for some time on bananas.

72

  1 9 02   R.R OS S

information on the subject. Once more I had to depend on myself; and I there-

fore took special note of the dappled-winged mosquitoes found near my la-

boratory. No less than four species were detected - a large brown species, a

large greenish one (with which the experiments just described were made), a

small black one, and a small brown one. The first was named later by Giles

from specimens brought to England by me, and was called by him Anopheles

rossi; 

and from the studies of Stephens and Christophers made in Calcutta

some years subsequently it is almost certain that the second species was A. fu-

liginosus.

Numerous specimens of Proteosoma in grey mosquitoes were sent to Man-

son on the 30th March.

By the middle of April I had overworked myself, and was obliged to ask for

ten days’ leave to the Himalayan hill-station Darjeeling, where I hoped for

time to write my report in a cool climate. I had heard also of several intensely

malarious spots at the foot of the Darjeeling mountains, and hoped to be able

to carry on there the studies on human malaria which were debarred in Cal-

cutta and at the same time to continue my work on avain malaria. I therefore

left Calcutta on the 17th April.

16. The Darjeeling Terai (April-June, 1898). Efforts to obtain assistance. 

The re-

sults with Proteosoma were obviously so important that it was necessary to give

them to the world at once, in the hope that many observers would now be

easily able to follow the work, and also that I might obtain assistance in con-

sequence of my success. Consequently I devoted my time at Darjeeling to

writing a report to my chief, the Director General of the Indian Medical Ser-

vice, on my latest work. The report begins with a brief statement of my first

discovery of the pigmented cells,* followed by a list of the experiments, both

positive and negative, which I had made with a view to infecting mosquitoes

with human malaria. Then comes a detailed account of experiments and posi-

tive results with Proteosoma, followed by a minute description of the neces-

sary technique, and of the appearance, position, and development of the pig-

mented cells. Next I discuss several points, including the bearing of MacCal-

lum’s work on mine. As I had brought my microscope and some of my speci-

mens with me, I was able to add to the report large plates giving drawings of

the pigmented cells up to the stage to which they had as yet been traced.** The

work was, however, hurriedly executed, as I had only a few days in which to

* In the twelfth line the word "ordinary" is a slip of the pen for "other".

** These plates are reproduced at the end of this publication.

    R E S E A R C H E S   O N   M A L A R I A

73

write it. The pigmented cells are called in it "proteosoma-coccidia", a term

which has been criticized. I thought at that time that the parasites of malaria

really belong to the Coccidiidae, the early stages of their life being passed in

man and birds, and the later stages (to which the name Coccidia might more

appropriately be attached) in the mosquito; just as the early and later stages of

the sexual forms of C. oviforme occur respectively in the bile ducts and the in-

testine of the rabbit. At the end of the report a description of the grey and

brindled mosquitoes with drawings is furnished by Mr. G. C. Dudgeon, a

gentleman who was acquainted with entomology; and the report concludes

Fig. 3. From paper by Manson, British Medical Journal, 18th June, 1898, p. 1577. (After Ross’s

drawings.)

74

    1 9 0 2   R . R O S S

with the words, "These observations prove the mosquito theory of malaria as

expounded by Dr. Patrick Manson..."

The report after some delay, was dated 21st May, and was despatched at

once, with an urgent request that it might be published as soon as possible. To

my surprise I was informed that publication was not allowed without the per-

mission of the Secretary of State for India. This meant writing to England and

several months delay; but the report was printed very soon and numerous

copies were sent at the end of June to Manson for private circulation among

persons interested in malaria. In the meantime my success had been described

in detail both to Laveran and Manson in letters dated 22nd April - the letters

being accompanied by a series of seventeen more preparations; and, as my

results could not be published by myself, I now asked Manson to publish them

for me.

On the 18th June Manson published an able paper on the subject. The article

commences with a resumé of my orginal discovery of pigmented cells in dap-

pled-winged mosquitoes fed on a human patient with malaria, and gives the

references to my papers describing the observation

41

. It goes on to describe the

new results with Proteosoma; giving drawings of the pigmented cells up to the

sixth day of development, and a diagram showing the connection between

MacCallum’s observation and my own; and it concludes with letters from

Nuttall and Laveran accepting my results. Laveran said, "It appears to me to

be undoubted that the elements discovered by Dr. R. Ross in the stomach of

mosquitoes fed on the blood of birds, the subjects of haemosporidiosis, are

really parasites, and that these parasites represent one of the phases of the evolu-

tion of the haematozoa... I have shown the preparations to M. Metchnikoff,

who shares my opinion".*

This paper drew general attention to my work, to which previously little

credence had been attached; and, as many of my preparations had been sent to

England and France, not only were those competent to form an opinion en-

abled to judge of the truth of my statements, but those who wished to follow

my steps were now easily able to do so. In fact a most amusing comedy now

commenced, in which we witnessed the hasty efforts of those who had been

sceptics, not only to follow my steps but to persuade the world that their la-

bours were original. During several years since that date every observation of

mine has been independently discovered by various writers.

Recognizing the vast significance of these preliminary results with Proteo-

* Owing to a misapprehension, this paper erroneously states that Halteridium also had

been cultivated.

    R E S E A R C H E S   O N   M A L A R I A

75

soma, 

and also feeling that it was quite beyond the power of one man to com-

plete as quickly as the interests of humanity demanded the work which re-

mained to be done, I now made strong efforts to obtain assistance. The help of

a single medical man to collect mosquitoes and cases of malaria for me would

certainly have enabled me to reach the last proofs in a month or two; and be it

remembered, the mortality from fever in India alone is said to amount to

something like ten thousand persons every day. When, however, I asked the

Director General for the services of one or more junior medical officers, I was

told that none could be spared at the time. As a matter of fact there are always

many medical officers in military employment in India, who can be spared if

they are urgently called for; and the truth is that the necessary trouble was not

taken. I then wrote to Manson begging him by all means in his power to ob-

tain assistance for me from England; and thought that the Royal Society,

which is subsided to a small amount by Government, might afford to give it.

The matter was considered; and it was finally agreed to appoint, with the help

of the Colonial Office, a commission of three gentlemen to investigate mala-

ria. Two of these were sent in the autumn to study the subject - in Italy; and,

after much difficulty, the third was allowed to come to me. He arrived at

Christmas with orders to stay for two months - not to help me but to verify

my statements!

That was all the help I received. The excuse is that my work had not been

confirmed. But it had been accepted by Laveran, Manson, Metchnikoff, and

Nuttall, who at least knew the subject. Was not this enough to justify the ex-

penditure of a few hundred pounds in so great a cause? I mention these facts

because it was largely this failure to obtain assistance which drove me from

India some months later; which delayed the completion of my work for more

than a year, and which postponed the adoption of an energetic prophylaxis in

India until the present. Not mine the fault: the truth is that for some inexpli-

cable reason men will never recognize the transcendent importance of investi-

gation into the causes of those great diseases which destroy them.

The rest of my time in this district was spent in making attempts to find a

suitable place in the intensely malarious areas at the foot of the mountains for

researches on human malaria. This alone was a matter of no little difficulty, as

the locality was new to me and I could obtain no accurate information regard-

ing the disease. I worked especially at a place called Punkabari, situated a few

hundred feet above the plain. A hospital and plantation existed here, and there

was a large village some miles away on the plain. But the results were not grati-

fying; few dappled-winged mosquitoes could be found, as the rainy season

76

    1 9 0 2   R . R O S S

had not yet commenced; while to my grief I discovered that the plague-scare

was, if anything, stronger here than in Calcutta. So terrified were the natives,

that on one occasion, when one of my men shot a sparrow for me in the vil-

lage, all the coolies in the neighbourhood ran away for miles into the jungles,

costing the planters much money and trouble before they could be induced to

return. In fact I was given to understand that scientific investigations were not

required there at the moment! Indeed it soon became apparent that I was only

wasting much valuable time; and I consequently determined to complete my

researches on Proteosoma at Calcutta without further delay.

17. Calcutta (June-August, 1898). The route of infection. 

On my return to Cal-

cutta (4th June) I found it still quite impossible to obtain cases of human mala-

ria for my work, and therefore proceeded at once with the life-history of Pro-

teosoma. 

The most wonderful of all the phases of this history was now to be

revealed. I had traced the development of the pigmented cells up to their ma-

turity and subsequent rupture and discharge of their contents into the body-

cavity of the grey mosquitoes. I could not see at the moment what happened

to these contents; yet upon this point depended the vastly important ques-

tion of the route of infection in malaria. But, when I had broken off my work

a few weeks previously, the contents had appeared to consist of little more than

a pure fluid.

Hitherto my mosquitoes had been dissected in water or a weak solution of

salt, and I had had no time for methodical staining. A strong salt solution was

now used and the secret was revealed. The contents of the mature pigmented

cells did not consist of clear fluid, but of a multitude of delicate thread-like

bodies, which, on the rupture of the parent cell, were poured into the body-

cavity of the insect, and which were evidently spores.

Fig. 4. Sketch of thread-like bodies (sporozoids or blasts) escaping from mature rup-

tured pigmented cell (zygote). From letter of Ross to Laveran, dated 18th July, 1898.

    R E S E A R C H E S   O N   M A L A R I A

77

What happened now to these spores in view of the theories mentioned in

section 12? Did they escape into the water according to Manson’s ideas; or

were they voided by the intestine according to mine; or did they in some

mysterious manner work their way into healthy persons during puncture,

according to the theories of King and Bignami and later of myself? But the

staff of theory was no longer necessary; plain research would suffice.

Here there was another sharp but short struggle. I saw that the thread-like

bodies, although apparently without motion themselves, were soon scattered

by the insect’s circulation all through its body; but beyond this I could not

follow them for some time, in spite of the most assiduous endeavours. They

seemed to have been created without object.

On the 2nd July however, I found in the thorax of a mosquito a large cell

which, surprising to state, contained within it several of the thread-like bodies.

They were able then to work their way into cells; but what was the cell? On

the 4th July, while working upon another mosquito, I found that the thread-

like bodies seemed to become more and more numerous towards a point in

the thorax - as if they were converging toward some destination. At that point

there were numerous cells such as I had seen on the 2nd July. They were at-

tached to a duct and were all contained within the same capsule - they con-

stituted in fact some kind of gland. In all these cells there were hundreds of the

thread-like bodies, floating loosely at all angles to each other like fish in globes

of glass. Close by was another lobe of the gland similarly full of the spores.

I was at the summit but not on it. I did not know what the gland was. I knew

the appearance of the cells it is true, but in spite of my thousand and more dis-

sections I had by no means acquired a full knowledge of the macroscopical

anatomy. I found it by no means easy to meet with the gland again. On the

8th July the mystery was solved. The gland lay in the neck and upper thorax-

Fig. 5. Thread-like bodies (sporozoids) in cells of salivary gland of mosquito. From  letter

of Ross to Laveran, dated 18th July, 1898.

78

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Fig. 6. Salivary gland of mosquito. From letter of Ross to Manson, dated 6th July, 1898.

the throat of the mosquito. It consisted of three lobes on each side. The ducts

of each lobe unite together like the midrifs of a trefoil. The duct so formed

runs forward and meets the similar duct of the other side under the chin - so to

speak - of the mosquito. The common duct advances still further and enters

through the round base of the central stylet or stabbing weapon of the mosqui-

to’s proboscis. It was easy now to recognize the nature of the gland; it was the

salivary gland, 

which secretes the irritating fluid which the mosquito injects in

the wound made by her in the skin, perhaps to dilate the vessels, perhaps to

prevent speedy coagulation of the blood.*

The exact route of infection of this great disease, which annually slays its

millions of human beings and keeps whole continents in darkness, was reveal-

ed. These minute spores enter the salivary gland of the mosquito and pass with

its poisonous saliva directly into the blood of men. Never in our dreams had

we imagined so wonderful a tale as this.

But still all this was inference only; the last proof was demanded. If the in-

fection can be given in this way, give it. I had long possessed in the laboratory

five old birds - four sparrows and one weaver-bird - which had been kept

there for my "control" experiments, because they had never been found to

contain Proteosoma, even after several examinations. On the 25th June, as soon

as I began to suspect the destination of the thread-like bodies, these birds were

all examined again, and were found to be still quite healthy. On that and the

following nights, a large number of grey mosquitoes which had been long

previously fed upon infected birds and many of which had been found to con-

* This gland had been discovered in 1888 by Macloskie

5

, but I did not know it at the time

and still had received no literature on the subject.

    R E S E A R C H E S   O N   M A L A R I A

79

tain the thread-like bodies in their salivary glands, were released within a mos-

quito-net in which the five healthy birds were placed. On the following

mornings I satisfied myself that the infected mosquitoes had gorged them-

selves freely on the birds; and then, fascinated by the study of the parasites in

the salivary glands of mosquitoes, I forgot all about even this important ex-

periment.

Now only a small percentage of birds in Calcutta are infected with Proteo-

soma. 

Out of 111 wild sparrows examined by me I found the parasites only in

15, or 13.5 per cent. Moreover, even in infected birds, the parasites were scarce,

seldom more than one being found in each field of the microscope. On the

9th July I suddenly remembered my experiment and examined the previously

healthy birds. All of them without exception were now found swarming with

Proteosoma, 

as many as twenty or even more being found in each field.

But not content even with this I repeated the experiment over and over

again; and within the next few weeks I succeeded in infecting 22 out of 28

healthy sparrows (79 per cent), and also a crow and four weaver-birds, and,

moreover, gave a more copious infection to four sparrows which previously

contained only a few parasites. At the same time I kept as controls a number

of healthy birds in mosquito-nets, safe from the bites of mosquitoes, and found

that none of them became infected (with one exception probably due to an

error).

Manson, to whom I had sent full details, told me that he would expound all

Fig. 7. Thread-like bodies (rods, sporozoids) in salivatory glands of mosquito. Published

from Ross’s drawing by Manson, British Medical Journal, 24th September, 1898, p. 852.

80

  1 9 0 2   R . R O S S

my results, with demonstrations of my specimens, at the meeting of the Brit-

ish Medical Association to be held at Edinburgh at the end of July. I now an-

nounced the successful infection of birds to him by a telegram, which reached

him just as he was setting out (though ill at the time) for the meeting; and he

was therefore able to communicate the complete life-history of the parasites

in his address.

His exposition as Dr. Charles said, "created quite a furore", and was quickly

made known everywhere. His paper was published on the 24th September

43

and gave a full account of the subject up to the infection of healthy birds, to-

gether with several drawings of the thread-like bodies, both free and in the

salivary glands, taken from my letters.

It was interesting during these researches to watch the gradual invasion of

the birds by the parasites. From five to eight days after they were bitten by in-

fected mosquitoes no parasites could be found in their blood; then a few ap-

peared; then many; and at the last large numbers. The first five birds all died,

and so did some of the others; and their liver was found to be full of the char-

acteristic pigment of malaria. But many recovered, the parasites gradually

decreasing in number.

At the same time I was temporally not a little delayed by finding inside the

mature pigmented cells certain large brown or black bodies which I provi-

sionally thought might be connected with their life-history. As proved by the

researches just described, malaria could be carried by mosquitoes from the

sick to the healthy, but as we know malaria clings intensely to location. It

therefore seemed not at all unlikely that these black bodies, occurring as they

did actually within the pigmented cells, might be of the nature of sporocysts

meant in some way to infect other mosquitoes - so that the infection might

not only be carried from man to man by the mosquito, but from mosquito to

mosquito; or they might be meant to infect man, as Manson had thought,

through the water. It was of course necessary, for sound science, to examine

these bodies; and I therefore tried to infect both birds and the larvae of mos-

quitoes by feeding them on insects containing these black spores; but the re-

sults were negative. Subsequently I saw reason to doubt whether the black

spores really had any connection with the parasites (section 20).

But there was little time for such researches, necessary as they seemed at the

moment. Although there could be no doubt that the human parasites have the

same history as Proteosoma, still it was a necessary formality to complete the

partial demonstration of this fact which had been already attained, if only to

persuade Government to take active measures against the disease; and I was at

    R E S E A R C H E S   O N   M A L A R I A 

81

last free to undertake the work. But now precisely occurred my last and most

annoying interruption.

Before coming to this, however, let us consider the results which had al-

ready been attained and which have been the basis of nearly all that has been

subsequently done.

(1) The general life-history of Proteosoma in the grey mosquito and the

mode of infection being now ascertained, we could foretell to a practical cer-

tainty that the life-history and mode of infection of all the other parasites of

the same group, including the human ones, would be closely similar in all

their stages; that is, that if they differed at all, they would differ only in small

details. The result of this was that if anyone wished to trace the life-history of

any of these organisms in a second host he would now find the task an ex-

tremely easy one, because (a) he would know exactly the appearance of the

parasite he was in search of, and (b) he would know exactly in what part of

the anatomy of the second host to look for it. And if he wished to ascertain

whether a given animal was or was not the second host of the parasite, he could

easily make sure of the fact by ascertaining whether or not it harboured the

described parasites, after feeding and dissection by the methods laid down by

me.

It is in fact solely by this means that we have been able to demonstrate the

proper hosts of the human parasites in many parts of the world.

(2) More than this, the pigmented cells of the aestivo-autumnal parasite of

man had been demonstrated to be exactly similar to those of Proteosoma on the

second, fourth, and fifth days after infection of the mosquito; and the hosts of

this important organism were shown to be at least two species of a special

genus which could be recognized by its possessing spotted wings and boat-

shaped eggs (section 23); and were clearly shown not to be my grey and

brindled mosquitoes, the former of which had been described sufficiently for

recognition

39,42

.

(3) The important law that not all species of mosquitoes can harbour a

given parasite of this group had been established, both with regard to the

aestivo-autumnal parasite and Proteosoma and Halteridium; and several im-

portant facts regarding mosquitoes had slowly become evident to me - but

were not published until later.

(4) Lastly full directions of technique had been given in my report

42

. These

consisted of numerous essential details, acquired during several years’ expe-

rience, regarding dissection and feeding, etc. - without a knowledge of which

the observer would be very likely to go wrong (as for instance by attempting

82

   1 9 0 2  R.R O S S

to section his mosquitoes for searching for the parasites, and omitting to feed

them regularly and change their soiled habitations for clean ones).

On the other hand my researches had given little or no information about

the quartan and tertian parasites - except of course the all important analogy

with Proteosoma. The observation of the grey mosquito caught feeding on the

case of tertian was doubtful (section 14). Moreover they had not directly and

absolutely demonstrated the final stages even of the aestivo-autumnal para-

sites in the dappled-winged mosquitoes, nor the mode of infection. But never-

theless they had reduced the demonstrations still required to an easy formality

which was within the capacity of any tyro with sufficient material and a mi-

croscope.

I am sorry to have to write such a summary of my work as this one; but it

is rendered necessary by those who, during the long interruption of my la-

bours which now followed, were able to work out some details of the subject

before me, and who have wished to conceal the assured fact that their efforts

were simply a repetition and imitation of mine. It should be pointed out that,

by a generally recognized zoological rule, the discovery of the life-history of

Proteosoma 

in mosquitoes covers that of other members of the same group of

organisms, which have precisely the same development. By that rule, the right

of priority in discovery belongs to him who first works out the life-history of

one species of a group of animals; not to those who merely perform the easy

task of extending the known facts to other species. Discovery is discovery; the

determination of parallel facts, the filling in of details, the publication of pretty

illustrations, and the furnishing of formal proofs of matters which are already

certain, are useful - but do not constitute discovery.

My infection experiments on birds were completed early in August, and, as

will be related presently, I was now no longer able to defer my work on  kala-

azar. 

Consequently I was obliged to leave Calcutta on the 13th August for my

new duties - much exhausted by work and heat in the plains. Before doing so,

however, I released my host of little feathered prisoners, which had unwil-

lingly been of such assistance in the investigation.

It should be mentioned that from the first discovery of the thread-like bod-

ies I had wondered whether they have any other destination besides the sali-

vary gland. The eggs were especially suspected, but the results of investigation

were negative. I therefore now concluded that malaria is communicated only

by the bites of insects.

RESEARCHES   ON   MALARIA 

83

 

18. Darjeeling district (August—September, 1898). Kala-dukh. It was mentioned 

at the end of section 14 that I myself had proposed to Government that kala- 

azar should be included in the programme of my year's special duty; because 

I then hoped that this disease might shed light upon the mosquito theory; but 

now when the theory was established and it was necessary to press on with the 

study of the human malaria, I wished to escape this additional duty, as I dread- 

ed lest it should involve me in much pathological work which would interfere 

with the principal line of research. I hinted as much to the Director General, 

but was told that he expected me to adhere to the programme. The disease 

was exciting much comment because it was new and was taking some thou- 

sand lives annually in Assam; but it was forgotten that malaria, though it is 

not new, takes some millions of lives annually in India alone! 

Harold Brown had recently studied a disease which existed at the foot of the 

Darjeeling mountains, and which was called kala-dukh  (black sickness) and 

was evidently closely allied to kala-azar (black fever). Consequently I obtained 

permission to investigate this disorder first, partly because an opportunity 

might be afforded me of making further studies at the same time on malaria 

in my old haunts at Punkabari. Fixing my head quarters at Kurseong in the 

hills on the road to Darjeeling, I made numerous visits to this locality, but was 

dogged by ill-luck. The plague-scare, though waning, was still present; and 

difficulties of transport impeded the work. On the 25th August I arrived at 

Naxalbari, an intensely malarious plantation and village on the plain beyond 

the foot of the hills, and found swarms of small and large dappled-winged 

mosquitoes (probably Anopheles listoni and  A. rossi). There was no time to 

make formal experiments, and the people would not have allowed them; but 

I examined some dozens of these mosquitoes caught in the houses of infected 

persons, both for the pigmented cells and the thread-like bodies; but without 

success.* Nearly all my time was however taken up in pathological enquiries 

on kala-dukh - as I feared would be the case. But now it was no longer possible 

to postpone the evil hour without dereliction of duty, and I was obliged to set 

out on the long journey to Assam. 

19.  Assam (September—November, 1898). Kala-azar. I arrived at Nowgong, 

the centre of the epidemic of kala-azar, on the 13th September. It was at once 

obvious that my worst fears were well-founded, and that I would be plunged 

* How unfortunate I was in this respect may be gathered from the papers of Stephens and 

Christophers

71

 who later found many of these mosquitoes