From "Manual of Muad'Dib" by the Princess Irulan

I am now a Reverend Mother , Jessica realized.
And she knew with a generalized awareness that she had become, in truth, precisely what was meant by a Bene Gesserit Reverend Mother. The poison drug had transformed her.
This wasn't exactly how they did it at the Bene Gesserit school, she knew. No one had ever introduced her to the mysteries of it, but she knew.
The end result was the same.
Jessica sensed the daughter-mote still touching her inner awareness, probed it without response.
A terrible sense of loneliness crept through Jessica in the realization of what had happened to her. She saw her own life as a pattern that had slowed and all life around her speeded up so that the dancing interplay became clearer.
The sensation of mote-awareness faded slightly, its intensity easing as her body relaxed from the threat of the poison, but still she felt that other mote, touching it with a sense of guilt at what she had allowed to happen to it.
I did it, my poor, unformed, dear little daughter, I brought you into this universe and exposed your awareness to all its varieties without any defenses .
A tiny outflowing of love-comfort, like a reflection of what she had poured into it, came from the other mote.
Before Jessica could respond, she felt the adab presence of demanding memory. There was something that needed doing. She groped for it, realizing she was being impeded by a muzziness of the changed drug permeating her senses.
I could change that , she thought. I could take away the drug action and make it harmless . But she sensed this would be an error. I'm within a rite of joining .
Then she knew what she had to do.
Jessica opened her eyes, gestured to the watersack now being held above her by Chani.
"It has been blessed," Jessica said. "Mingle the waters, let the change come to all, that the people may partake and share in the blessing."
Let the catalyst do its work , she thought. Let the people drink of it and have their awareness of each other heightened for awhile. The drug is safe now . . . now that a Reverend Mother has changed it .
Still, the demanding memory worked on her, thrusting. There was another thing she had to do, she realized, but the drug made it difficult to focus.
Ah-h-h-h-h . . . the old Reverend Mother .
"I have met the Reverend Mother Ramallo," Jessica said. "She is gone, but she remains. Let her memory be honored in the rite.
Now, where did I get those words? Jessica wondered.
And she realized they came from another memory, the life that had been given to her and now was part of herself. Something about that gift felt incomplete, though.
"Let them have their orgy ," the other-memory said within her. "They've little enough pleasure out of living. Yes, and you and I need this little time to become acquainted before I recede and pour out through your memories. Already, I feel myself being tied to bits of you. Ah-h-h, you've a mind filled with interesting things. So many things I'd never imagined."
And the memory-mind encapsulated within her opened itself to Jessica, permitting a view down a wide corridor to other Reverend Mothers until there seemed no end to them.
Jessica recoiled, fearing she would become lost in an ocean of oneness. Still, the corridor remained, revealing to Jessica that the Fremen culture was far older than she had suspected.
There had been Fremen on Poritrin, she saw, a people grown soft with an easy planet, fair game for Imperial raiders to harvest and plant human colonies on Bela Tegeuse and Salusa Secundus.
Oh, the wailing Jessica sensed in that parting.
Far down the corridor, an image-voice screamed: "They denied us the Hajj!"
Jessica saw the slave cribs on Bela Tegeuse down that inner corridor, saw the weeding out and the selecting that spread men to Rossak and Harmonthep. Scenes of brutal ferocity opened to her like the petals of a terrible flower. And she saw the thread of the past carried by Sayyadina after Sayyadina—first by word of mouth, hidden in the sand chanteys, then refined through their own Reverend Mothers with the discovery of the poison drug on Rossak . . . and now developed to subtle strengthen Arrakis in the discovery of the Water of Life.
Far down the inner corridor, another voice screamed: "Never to forgive! Never to forget!"
But Jessica's attention was focused on the revelation of the Water of Life, seeing its source: the liquid exhalation of a dying sandworm, a maker. And as she saw the killing of it in her new memory, she suppressed a gasp.
The creature was drowned!
"Mother, are you all right?"
Paul's voice intruded on her, and Jessica struggled out of the inner awareness to stare up at him, conscious of duty to him, but resenting his presence.