found a creature which would multiply enormously and with a fine
versatility upon the wastes of our human cities. True, it smelled like
an ancient Earth-animal called skunk--butyl mercaptan. It was not
pretty--to most eyes it is revolting. But it was a scavenger and there
was no waste product it would not devour."

Dr. Lett turned from the culture oven. He had a plastic container in
his hand. A faint, disgusting odor spread from it.

"You ask what the delusions of para may be?" he grinned derisively. He
held out the container. "It is the delusion that this scavenger, this
eater of unclean things, this unspeakable bit of slimy, squirming
flesh--paras have the delusion that it is the most delectable of
foodstuffs!"

He thrust the plastic container under Calhoun's nose. Calhoun did not
draw in his breath while it remained there. Dr. Lett said in mocking
admiration:

"Ah! You have the strong stomach a medical man should have! The
delusion of the para is that these squirming, writhing objects are
delightful! Paras develop an irresistible craving for them! It is as
if men on an Earth-like world develop an uncontrollable hunger for
vultures and rats and--even less tolerable things. These
scavengers--paras eat them! So normal men would rather die than become
paras!"

* * * * *

[Illustration]

Calhoun gagged in purely instinctive revulsion. The things in the
plastic container were gray and small. Had they been still, they might
have been no worse to look at than raw oysters in a cocktail. But they
squirmed. They writhed.

"I will show you," said Dr. Lett amiably.

He turned to the glass plate which divided the room into halves. The
man behind the thick glass now pressed eagerly against it. He looked
at the container with a horrible, lustful desire. The thick-eyeglassed
man clucked at him, as if at a caged animal one wishes to soothe. The
man beyond the glass yawned hysterically. He seemed to whimper. He
could not take his eyes from the container in the doctor's hands.

"So!" said Dr. Lett.

He pressed a button. A lock-door opened. He put the container inside
it. The door closed. It could be sterilized before the door on the
other side would open, but now it was arranged to sterilize itself to
prevent contagion from coming out.

The man behind the glass uttered inaudible cries. He was filled with
beastly, uncontrollable impatience. He cried out at the mechanism of
the contagion-loc