at the man before him
looked in exceptionally good health for one who had been on a marginal
diet for two weeks. "Then what _have_ you been living on?"

"The monkey food, sir."

"_Monkey food?_"

"Yessir. Them greenish things with the purple spots. You know--them
fruits you feed the monkeys on."

Pilar looked at MacNeil goggle-eyed for a full thirty seconds before he
burst into action.

* * * * *

"No, of course I won't punish him," said Colonel Fennister. "Something
will have to go on the record, naturally, but I'll just restrict him to
barracks for thirty days and then recommend him for light duty. But are
you _sure_?"

"I'm sure," said Pilar, half in wonder.

Fennister glanced over at Dr. Smathers, now noticeably thinner in the
face. The medic was looking over MacNeil's record. "But if that fruit
kills monkeys and rats and guinea pigs, how can a _man_ eat it?"

"Animals differ," said Smathers, without taking his eyes off the record
sheets. He didn't amplify the statement.

The colonel looked back at Pilar.

"That's the trouble with test animals," Dr. Pilar said, ruffling his
gray beard with a fingertip. "You take a rat, for instance. A rat can
live on a diet that would kill a monkey. If there's no vitamin A in the
diet, the monkey dies, but the rat makes his own vitamin A; he doesn't
need to import it, you might say, since he can synthesize it in his own
body. But a monkey can't.

"That's just one example. There are hundreds that we know of and God
alone knows how many that we haven't found yet."

Fennister settled his own body more comfortably in the chair and
scratched his head thoughtfully. "Then, even after a piece of alien
vegetation has passed all the animal tests, you still couldn't be sure
it wouldn't kill a human?"

"That's right. That's why we ask for volunteers. But we haven't lost a
man so far. Sometimes a volunteer will get pretty sick, but if a food
passes all the other tests, you can usually depend on its not killing a
human being."

"I gather that this is a pretty unusual case, then?"

Pilar frowned. "As far as I know, yes. But if something kills all the
test animals, we don't ask for humans to try it out. We assume the worst
and forget it." He looked musingly at the wall. "I wonder how many
edible plants we've by-passed that way?" he asked softly, half to
himself.

"What are you going to do next?" the colonel asked. "My men are getting
hungry."