Rose said, "Why particularly Earthmen?"
Drake simply stood apart, intent, asking no further questions. He was content, apparently, to let the Hawkinsite speak.
"Have you not surmised that the sixth intelligence is a native of Earth? Mankind from the beginning has lived with it, has adapted to it, is unconscious of it. It is why the higher species of terrestrial animals, including man, do not grow after maturity and, eventually, die what is called natural death. It is the result of this universal parasitic infestation. It is why you sleep and dream, since it is then that the parasitic mind must feed and then that you are a little more conscious of it, perhaps. It is why the terrestrial mind alone of the intelligences is so subject to instability. Where else in the Galaxy are found split personalities and other such manifestations? After all, even now there must be occasional human minds which are visibly harmed by the presence of the parasite.
"Somehow, these parasitic minds could traverse space. They had no physical limitations. They could drift between the stars in what would correspond to a state of hibernation. Why the first ones did it, I don't know; probably no one will ever know. But once those first discovered the presence of intelligence on other planets in the Galaxy, there was a small, steady stream of parasitic intelligences making their way through space. We of the outer worlds must have been a gourmet's dish for them or they would have never struggled so hard to get to us. I imagine many must have failed to make the trip, but it must have been worth the effort to those who succeeded.
"But you see, we of the other worlds had not lived with these parasites for millions of years, as man and his ancestors had. We had not adapted ourselves to it. Our weak strains had not been killed off gradually through hundreds of generations until only the resistants were left. So, where Earthmen could survive the infection for decades with little harm, we others die a quick death within a year."
"And is that why the incidence has increased since interstellar travel between Earth and the other planets has begun?"
"Yes." For a moment there was silence, and then the Hawkinsite said with a sudden access of energy, "Give me back my cylinder. You have your answer."
Drake said, coolly, "What about the Missing Persons Bureau?" He was swinging the cylinder again; but now the Hawkinsite did not follow its movements. The gray translucent film on his eyes had deepened and Rose wondered whether that was simply an expression of weariness or an example of the changes induced by cyanide lack.
The Hawkinsite said, "As we are not well adapted to the intelligence that infests man, neither is it well adapted to us. It can live on us-it even prefers to, apparently-but it cannot reproduce with ourselves alone as the source of its life. The Inhibition Death is therefore not directly contagious among our people."
Rose looked at him with growing horror. "What are you implying, Dr. Tholan?"
"The Earthman remains the prime host for the parasite. An Earthman may infect one of us if he remains among us. But the parasite, once it is located in an intelligence of the outer worlds, must somehow return to an Earthman, if it expects to reproduce. Before interstellar travel, this was possible only by a re-passage of space and therefore the incidence of infection remained infinitesimal. Now we are infected and reinfected as the parasites return to Earth and come back to us via the mind of Earthmen who travel through space."
Rose said faintly, "And the missing persons-"
"Are the intermediate hosts. The exact process by which it is done, I, of course, do not know. The masculine terrestrial mind seems better suited for their purposes. You'll remember that at the Institute I was told that the life expectancy of the average human male is three years less than that of the average female. Once reproduction has been taken care of, the infested male leaves, by spaceship, for the outer worlds. He disappears."
"But this is impossible," insisted Rose. "What you say implies that the parasite mind can control the actions of its host! This cannot be, or we of Earth would have noticed their presence."
"The control, Mrs. Smollett, may be very subtle, and may, moreover, be exerted only during the period of active reproduction. I simply point to your Missing Persons Bureau. Why do the young men disappear? You have economic and psychological explanations, but they are not sufficient. -But I am quite ill now and cannot speak much longer. I have only this to say. In the mental parasite, your people and mine have a common enemy. Earthmen, too, need not die involuntarily, except for its presence. I thought that if I found myself unable to return to my own world with my information because of the unorthodox methods I used to obtain it, I might bring it to the authorities on Earth, and ask their help in stamping out this menace. Imagine my pleasure when I found that the husband of one of the biologists at the Institute was a member of one of Earth's most important investigating bodies. Naturally, I did what I could to be made a guest at his home in order that I might deal with him privately; convince him of the terrible truth; utilize his position to help in the attack on the parasites.
"This is, of course, now impossible. I cannot blame you too far. As Earthmen, you cannot be expected to understand the psychology of my people. Nevertheless, you must understand this. I can have no further dealing with either of you. I could not even bear to remain any longer on Earth."
Drake said, "Then you alone, of all your people, have any knowledge of this theory of yours."
"I atone."
Drake held out the cylinder. "Your cyanide, Dr. Tholan."
The Hawkinsite groped for it eagerly. His supple fingers manipulated the hose and the needle valve with the utmost delicacy. In the space of ten