Needle

"You may be right, but that will no longer be true for this one you just saw. He must be examined before he leaves! Start thinking, please."

For the first time that day Bob completely forgot his sunburn as he walked back up the road.

Chapter X. MEDICAL REPORT

BOB MANAGED to hide his concern at lunch; his mother had thought of something during the morning to take his mind off the new problem. She had been wondering how to persuade her son to have a checkup by the island doctor, and had realized just after he disappeared what a splendid excuse the sunburn provided. She had no opportunity to discuss it with her husband, since Bob had arrived home first, but he would probably have agreed with her anyway. She brought up the subject as they finished the meal.

She did not really expect to win without argument; she knew Bob was ashamed of having acquired the sunburn and did not want more people than were strictly necessary to know about it. She was therefore somewhat astonished when her son agreed without a murmur to the suggestion that he drop into the doctor's office that afternoon, though she had the control and presence of mind not to show it.

The fact of the matter was that Bob had been thinking about the Hunter's failure to answer certain of his questions, particularly those which dealt with the details of how he was to recognize his quarry and still more, what he was to do after the creature was found. If the Hunter knew, well and good; but the suspicion that his invisible guest did not know was growing. It followed that Bob must get some ideas of his own; and for such ideas to be any use, he must learn more about the Hunter's species. The alien had said he resembled a virus. Very well. Bob would find out about viruses, and the logical place to do that was in a doctor's office. He had known it would be somewhat out of character for him to make the suggestion himself, but it did not occur to him to wonder that his mother should have done so; he simply accepted it as a piece of luck.

Dr. Seever knew Bob very well—as he knew every other person born on the island. He had read the communication from the school doctor, and agreed with Mr. Ki

"Good heavens! You really celebrated getting back here, didn't you?"

"Don't rub it in, Doc. I really know better."

"I should think so. Well, well tan your hide for you- not the way it ought to be done, but you'll be more comfortable." The doctor set briskly to work, talking steadily the while. "You certainly aren't the fellow you used to be. I can remember when you were one of the most thoughtful and careful people here. Have you been sick lately at that school of yours?" Bob had not expected the question so soon or in just this form, but he had made plans for putting it to his own use when it came,

"Certainly not. You can look me over all day and won't find any germs at work."

Dr. Seever looked over his glasses at the boy. "That's certainly possible, I know, but is hardly assurance that nothing is wrong. It was not germs that caused that sunburn, you know."

"Well, I sprained an ankle and had a cut or two, but they don't count. You were talking about sickness, and you could find out about that with your microscope, couldn't you?"

The doctor smiled, conceiving that he knew what the boy was driving at "It's nice to find someone with such touching faith in medical science," he said, "but I'm afraid I couldn't. Just a minute and I'll show you why." He finished applying the sunburn material, put the container away, and brought an excellent microscope out of its cabinet Some searching among rather dusty slide files found what he wanted, and he began slipping the bits of glass onto the stage one after another as he talked.

"This one we can see, and recognize, easily. It's protozoan-an amoeba, of the type that causes a disease called dysentery. It's big, as disease-causing organisms run."

"I've seen them in bio class at school," Bob admitted, "but I didn't know they caused disease."

"Most of them don't. Now this"-the doctor slipped another slide under the objective-"is a good deal smaller. The other wasn't really a germ at all. This causes typhoid fever when it gets a chance, though we haven't had a case in a long time. The next is smaller still and is the cause of cholera."

"It looks like a sausage with the string still on one end," Bob remarked as he raised his head from the instrument.

"You can see it better with the high-powered objective in place," Dr. Seever remarked, turning the turret at the lower end of the instrument and sinking back into his chair while Bob looked once more.

"That's about as far as this gadget can go. There are many smaller bacteria-some of them harmless, some not. There is a class of things called Rickettsia which are smaller still and may not be bacteria at all, and there are viruses."

Bob turned from the microscope and attempted the difficult feat of looking interested without showing that the conversation had finally reached the point he wished.

"Then you can't show me a virus?" he asked, knowing the answer perfectly well.

"That's what I'm getting at A few of them have been photographed with the aid of the electron microscope- they seem to look a little like that cholera bug I showed you-but that's all. As a matter of fact, the word 'virus' was simply a confession of ignorance for a long time; doctors were blaming diseases which seemed to be life-caused for one reason of another, but for which they could find no causative organism such as I've shown you, on what they called 'filterable viruses'-so named because no matter how fine a filter you squeezed the juice from a diseased creature through, the cause seemed to go through with it They even found ways to separate the virus stuff chemically and crystallize it; it would still cause the same disease when the crystals were dissolved in water again. They devised a lot of very pretty experiments to guess at the sizes of the things, and their shapes, and other such matters long before they saw *em. Some scientists thought -and still think-they are single molecules; big ones, of course-even bigger than the albumin ones-that's the white of egg, you know. I have read several darn good books on the subject; you might like to do the same."

"I would," replied Bob, still trying not to seem too eager. "Do you have any of them here?" The doctor got out of his chair and rummaged through another cabinet, eventually emerging with a thick volume, through which he leafed rapidly.

"There's a good deal here but I'm afraid it's a bit technical. You may take it if you want, of course. I had another that was much better in every way from your standpoint, but I guess I've already let it out"

"Who has it?"

One of your friends, as I recall-young Norman Hay. He's been getting interested in biology lately. Maybe you heard about his trying to get to the museum on Tahiti. I don't know whether he's after my job or Ranee's over at the lab. He's had the book quite a while-several months, I think; if you can get it from him, take it"

"Thanks; I will." Bob meant the statement earnestly. "You couldn't tell me offhand more about the chemical separation you mentioned, could you? It sounds fu

"As I said, there's some doubt as to whether we should call the viruses living creatures. However, there's nothing unusual about the tests you mention. Haven't you ever heard of serums?"

"Yes, but I thought they were stuff that you used to make a person immune to some disease."

"That is frequently the case. However, a better way of looking at them is more or less as chemical fingerprints. The tissues of one type of creature try to fight off serums made from the tissues of another. You can get an animal used to human serum, for example, and then tell from the reaction between the serum of that animal and some unknown substance whether the substance contained human tissues or not. The details vary, of course, but that's one way of telling whether a bloodstain or other organic trace came from a man or some other animal."