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. Kinnaird’s opinion of it; but he was glad of the chance to see the boy himself. Even he, however, was a little startled when he saw the color of Bob’s skin.

“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 funny, identifying a living creature by chemistry.”

“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.”

“I see-I guess.” Bob’s eyes were narrowed in thought “Does this book have anything about that?”

“No. I can give you something on it, but I warn you it’s a little beyond high-school chemistry. Whose job are you after?”

“What? Oh, I see. Not yours, anyway. There was a problem I ran across, and I’d like to solve it myself if I can. If I can’t, I’ll be back for more help, I expect. Thanks, Doc.”

Seever nodded and turned back to his desk as Bob went out; and for several minutes the doctor meditated.

The boy was certainly more serious than he had been. It would be nice to know just what his problem was. Very possibly-even probably-it accounted for the personality change that had worried the school authorities. That, at least, would be a comforting report to give the boy’s father; and that, later in the afternoon, was just what the doctor did.

“I don’t think you need worry at all, Art, if you were. The kid’s gotten himself interested to the hilt in something that appears to have a scientific flavor-young Hay did the same a few months ago-and will simply soak it into his system. You probably acted the same, the last time you learned something big. He’s presumably going to change the world, and you’ll hear about it in due time.”

Bob had no intention of changing the world to any great extent, not even the human portion of it. However, some problems which had arisen in the course of the afternoon’s talk might make changes to individuals necessary, and once out of the doctor’s office he wasted no time in putting them up to the Hunter.

“Can we use that serum trick of the doc’s?”

“I doubt it. I am familiar with the technique, and know that since I have been with you so long your own blood serum might serve if it were not for one fact; but we would still have to decide where to use it If we could do that, I could make the exploration faster by personal contact.”

“I suppose that’s true. Still, you wouldn’t have to leave me-I might be able to make the check myself.”

“You have a point there. We will bear the possibility in mind. Have you any idea about getting at young Teroa? When will he be leaving?”

“The tanker comes every eight days, which means it’s due back a week from today. I suppose he’ll be going then; certainly not any sooner. I don’t think the Beam is around.”

“The Beam?”

“She’s a yacht owned by one of the company bigwigs, who sometimes comes to look things over. I left on her last fall-that’s why we were so far from the island when you first looked around. Come to think of it, I know she’s not near; she went into drydock in Seattle last fall, to get some sort of diving gear built into her bottom, and is there yet. I suppose you were going to ask who could have left on her while we were gone.”

“Correct. Thanks for settling the question so quickly.” The Hunter would have smiled had he been able.

Bob had no watch but was pretty sure it was nearly time for school to be dismissed, so he headed in that direction. He was early, and had to wait outside; but presently his friends came pouring out, giving vent to expressions of envy as they saw him.

“Never mind about how lucky I am not to be in school,” Bob said. “Let’s get to work on that boat. I’ve got to go back to school myself on Monday, and I’d like to have some fun first.”

“You’ve brought us luck, anyhow,” said Hay. “We’d been looking for a plank for weeks and didn’t find one until you got here. What say, fellows? Hadn’t we better get that thing into the boat while the luck holds?” There was a chorus of agreement and a general movement to collect bicycles. Bob rode on Malmstrom’s handle bars-he had walked to the doctor’s-as far as his own house, where he picked up his own machine and some tools. They waited at the culvert while Malmstrom and Colby went onto their respective dwellings for equipment; when they returned, the bicycles were left, shoes removed, and trousers rolled up. There was a path from the road down to the place the boat was kept, but it ran through the shallower parts of the creek in spots to avoid the undergrowth, and the boys had never bothered to construct bridges.

Splashing and crashing through water and bushes, they finally dumped their collection of tools at the point where the little watercourse emptied into the lagoon. The boat was there drawn up on the sand, with the plank beside it. The boys were relieved to see the latter; there had been no risk of anyone’s borrowing the boat, of course, even had it not been in its present condition, but the wood was another matter. The statement that Colby had stepped through the floor of the boat had been no exaggeration- a strip of planking four inches wide and more than two feet long was missing from the flat bottom.

The boys were not professional carpenters, but they had the boat turned over and the defective plank removed from its full length in record time. They found, however, that replacing the plank from the enormous board they had found was not such an easy matter. The first attempt came out too narrow in several places, because of their inability to saw straight near the line of the grain. The second try was started too wide, and after a good deal of labor with the plane was eventually reduced to a good fit. They had carefully salvaged the screws from the former piece and succeeded in attaching the replacement securely enough to satisfy them.

They immediately dragged the boat down to the water, brought the oars from the bushes, and the entire party piled in. The idea of letting the new plank soak for a while in order to swell, or at least to permit a guess at the seaworthiness of the new joints, occurred to them, but they were all excellent swimmers and much too impatient to hold up for any such consideration. There was some leakage at the seams, but it did not amount to more than the coconut-shell bailers could handle. The two youngest boys wielded these while Bob and Shorty rowed and Rice handled the tiller.

Bob suddenly realized that the figure which usually occupied the bow on these occasions was missing. Thinking back, he realized that this had been the case ever since his return. He spoke to Rice, who was facing him. “What’s become of Tip? I haven’t seen him since I got back.”

“No one knows.” The redhead’s face clouded over. “He just disappeared quite a long time ago-well before Christmas. We’ve looked all over the place for him. I’m afraid he must have tried to swim over to the islet where Norm has his tank-we sometimes went there without him- and got picked off by a shark, though it doesn’t seem very likely. The swim would be only a few yards, and I’ve never seen a live shark that close to shore. He just vanished.”

“That’s queer. Have you looked in the woods?”

“Some. You can’t search there very well. Still, if he’d been there alive, he’d have heard us; and I can’t think of anything that would hurt him there.”

Bob nodded, and spoke half to himself. “That’s right, come to think of it; there aren’t even any snakes here.” More loudly he asked, “What’s this about Norm’s tank? Is he going into competition with Pacific Fuels?”

“Course not,” returned Hay, looking up from his job of bailing. “I cleaned out one of the pools on the reef a little way from the beach and fenced it off, and have been putting things in it to make an aquarium. I did it just for fun at first, but there are some magazines that want pictures of sea life, and I’ve sent for some color film. Trouble is, nothing seems to live very long in the pool; even the coral dies.”

“I suppose you haven’t seen it since the boat was out. Let’s go over now and have a look.”

“I’ve been swimming over every day or two with Hugh or Shorty. It’s still not doing so well. I don’t know whether we could get there and back now before supper; we must have been working a long tune on the boat, and the sun’s getting down a bit.” The other boys looked up, noticing this fact for the first tune; their parents had long since given up trying to keep them from exploring any part of the island inside the reef, but they had some sort of regulation about meeting mealtimes. Without further remark Rice headed the boat back toward the creek, and the rowers began to take longer strokes.

Bob rowed without thinking much. Everywhere he turned there was lots to see, but none of it seemed to bear on his problem; the Hunter seemed to feel that Teroa should be tested, of course, but even he had no definite suspicion-it was simply that the boy was going out of reach. The thought reminded him of the talk he had had with Charlie that morning; he wondered whether the Polynesian boy had found Rice during the lunch hour.

“Anyone seen Charlie Teroa today?” he asked.

‘”No.” It was Malmstrom who answered. “He comes a couple of days a week for navigation, but this isn’t one of them. Think he’ll ever use it?”

“Not for anyone who knows him.” Rice’s voice was scornful. I’d rather hire someone likely to stay awake on the job.”

Bob concealed a smile. “He seems to get some work done in that garden of his,” he remarked.

“Sure, with his mother watching and his sisters helping. Why, he went to sleep with a boatload of dynamite last fall, when they were clearing the east passage.”

“You’re crazy!”

“That’s what you think. They sent him in alone for a case, and told him to stand by when he got back, and twenty minutes later my father found him moored to a bush on the reef, sound asleep, using the case for a foot-rest. He was lucky there weren’t caps aboard and that he wasn’t where a wave could have knocked the boat into the reef.”

“Maybe that wasn’t luck,” Bob pointed out. “He knew he didn’t have caps, and figured it was safe enough where he was.”

“Maybe; but I haven’t let him live it down yet.” Rice grinned mischievously.

Bob looked at the redhead, who was rather short for his age. “Someday he’ll throw you in the drink, if you don’t stop riding him. Besides, wasn’t that stowaway business your idea?”

Rice could have asked with some justice, what that had to do with matters, but he just chuckled and said nothing. A moment later the boat’s flat bottom grated on the beach.