“My dear Mr. Baley, I was very interested in your deductions. As for being off the case, I doubt it. Before the Commissioner left, I made a special point of asking that you be retained. I believe he will co-operate.”

Baley sat down, not entirely voluntarily. He said, sharply, “Why?” Dr. Fastolfe crossed his legs and sighed. “Mr. Baley, in general I have met two kinds of City dwellers, rioters and politicians. Your Commissioner is useful to us, but he is a politician. He tells us what we want to hear. He handles us, if you know what I mean. Now you came here and boldly accused us of tremendous crimes and tried to prove your case. I enjoyed the process. I found it a hopeful development.”

“How hopeful?” asked Baley sardonically.

“Hopeful enough. You are someone I can deal with frankly. Last night, Mr. Baley, R. Daneel reported to me by shielded subether. Some things about you interested me very much. For instance, there was the point concerning the nature of the book-films in your apartment.”

“What about them?”

“A good many dealt with historical and archaeological subjects. It makes it appear that you are interested in human society and that you know a little about its evolution.”

“Even policemen can spend their free time on book-films, if they so choose.”

“Quite. I’m glad of your choice in viewing matter. It will help me in what I am trying to do. In the first place, I want to explain, or try to, the exclusivism of the men of the Outer Worlds. We live here in Spacetown; we don’t enter the City; we mingle with you City dwellers only in a very rigidly limited fashion. We breathe the open air, but when we do, we wear filters. I sit here now with filters in my nostrils, gloves on my hands, and a fixed determination to come no closer to you than I can help. Why do you suppose that is?”

Baley said, “There’s no point in guessing.” Let him talk now.

“If you guessed as some of your people do, you would say that it was because we despised the men of Earth and refused to lose caste by allowing their shadow to fall upon us. That is not so. The true answer is really quite obvious. The medical examination you went through, as well as the cleansing procedures, were not matters of ritual. They were dictated by necessity.”

“Disease?”

“Yes, disease. My dear Mr. Baley, the Earthmen who colonized the Outer Worlds found themselves on planets entirely free of Terrestrial bacteria and viruses. They brought in their own, of course, but they also brought with them the latest medical and microbiological techniques. They had a small community of micro-organisms to deal with and no intermediate hosts. There were no mosquitoes to spread malaria, no snails to spread schistosomiasis. Disease agents were wiped out and symbiotic bacteria allowed to grow. Gradually, the Outer Worlds became disease-free. Naturally, as time went on, entrance requirements for immigrant Earthmen were made more and more rigorous, since less and less could the Outer Worlds endure the possible introduction of disease.”

“You’ve never been sick, Dr. Fastolfe?”

“Not with a parasitic disease, Mr. Baley. We are all liable to degenerative diseases such as atheroschlerosis, of course, but I have never had what you would call a cold. If I were to contract one, I might die of it. I’ve built up no resistance to it whatsoever. That’s what’s wrong with us here in Spacetown. Those of us who come here run a definite risk. Earth is riddled with diseases to which we have no defense, no natural defense. You yourself are carrying the germs of almost every known disease. You are not aware of it, since you keep them all under control at almost all times through the antibodies your body has developed over the years. I, myself, lack the antibodies. Do you wonder that I come no closer to you? Believe me, Mr. Baley, I act aloof only in self-defense.”

Baley said, “If this is so, why isn’t the fact made known on Earth? I mean, that it is not just queasiness on your part, but a defense against an actual physical danger.”

The Spacer shook his head. “We are few, Mr. Baley, and are disliked as foreigners anyway. We maintain our own safety on the basis of a rather shaky prestige as a superior class of being. We cannot afford to lose face by admitting that we are afraid to approach an Earthman. Not at least until there is a better understanding between Earthmen and Spacers.”

“There won’t be, on present terms. It’s your supposed superiority that we—they hate you for.”

“It is a dilemma. Don’t think we aren’t aware of it.”

“Does the Commissioner know of this?”

“We have never explained it to him flatly, as I have just done to you. He may guess it, however. He is quite an intelligent man.”

“If he guessed it, he might have told me,” Baley said reflectively.

Dr. Fastolfe lifted his eyebrows. “If he had, then you wouldn’t have considered the possibility of R. Daneel being a human Spacer. Is that it?”

Baley shrugged slightly, tossing the matter to one side.

But Dr. Fastolfe went on, “That’s quite true, you know. Putting the psychological difficulties to one side, the terrible effect of the noise and crowds upon us, the fact remains that for one of us to enter the City is the equivalent of a death sentence. It is why Dr. Sarton initiated his project of humanoid robots. They were substitute men, designed to enter the City instead of us—”

“Yes. R. Daneel explained this to me.”

“Do you disapprove?”

“Look,” said Baley, “since we’re talking to one another so freely, let me ask a question in simple words. Why have you Spacers come to Earth anyway? Why don’t you leave us alone?”

Dr. Fastolfe said, with obvious surprise, “Are you satisfied with life on Earth?”

“We get along.”

“Yes, but for how long will that continue? Your population goes up continuously; the available calories meet the needs only as a result of greater and greater effort. Earth is in a blind alley, man.”

“We get along,” repeated Baley stubbornly.

“Barely. A City like New York must spend every ounce of effort getting water in and waste out. The nuclear power plants are kept going by uranium supplies that are constantly more difficult to obtain even from the other planets of the system, and the supply needed goes up steadily. The life of the City depends every moment on the arrival of wood pulp for the yeast vats and minerals for the hydroponic plants. Air must be circulated unceasingly. The balance is a very delicate one in a hundred directions, and growing more delicate each year. What would happen to New York if the tremendous flow of input and outgo were to be interrupted for even a single hour?”

“It never has been.”

“Which is no security for the future. In primitive times, individual population centers were virtually self-supporting, living on the produce of neighboring farms. Nothing but immediate disaster, a flood or a pestilence or crop failure, could harm them. As the centers grew and technology improved, localized disasters could be overcome by drawing on help from distant centers, but at the cost of making ever larger areas interdependent. In Medieval times, the open cities, even the largest, could subsist on food stores and on emergency supplies of all sorts for a week at least. When New York first became a City, it could have lived on itself for a day. Now it cannot do so for an hour. A disaster that would have been uncomfortable ten thousand years ago, merely serious a thousand years ago, and acute a hundred years ago would now be surely fatal.”

Baley moved restlessly in his chair. “I’ve heard all this before. The Medievalists want an end to Cities. They want us to get back to the soil and to natural agriculture. Well, they’re mad; we can’t. There are too many of us and you can’t go backward in history, only forward. Of course, if emigration to the Outer Worlds were not restricted—”