one healthy in his mind," he
admitted. "It works pretty well. It satisfies all my mental appetites.
But naturally there are instincts--"

[Illustration]

She waited. He did not finish.

"What do you do about instincts that work and music and such things
can't satisfy?"

Calhoun grinned wrily;

"I'm stern with them. I have to be."

He stood up and plainly expected her to go into the other cabin for the
night. She did.

* * * * *

It was after breakfast-time of the next ship-day when he got out the
sample of clear liquid he'd worked so long to produce. "We'll see how it
works," he observed. "Murgatroyd's handy in case of a slip-up. It's
perfectly safe so long as he's aboard and there are only the two of us."

She watched as he injected half a cc under his own skin. Then she
shivered a little.

"What will it do?"

"That remains to be seen." He paused a moment. "You and I," he said with
some dryness, "make a perfect test for anything. If you catch something
from me, it will be infective indeed!"

She gazed at him utterly without comprehension.

He took his own temperature. He brought out the folios which were his
orders, covering each of the planets he should give a standard Medical
Service inspection. Weald was there. Dara wasn't. But a Med Service man
has much freedom of action, even when only keeping up the routine of
normal Med Service. When catching up on badly neglected operations, he
necessarily has much more. Calhoun went over the folios.

Two hours later he took his temperature again. He looked pleased. He
made an entry in the ship's log. Two hours later yet he found himself
drinking thirstily and looked more pleased still. He made another entry
in the log and matter-of-factly drew a small quantity of blood from his
own vein and called to Murgatroyd. Murgatroyd submitted amiably to the
very trivial operation Calhoun carried out. Calhoun put away the
equipment and saw Maril staring at him with a certain look of shock.

"It doesn't hurt him," Calhoun explained. "Right after he's born there's
a tiny spot on his flank that has the pain-nerves desensitized.
Murgatroyd's all right. That's what he's for!"

"But he's--your friend!"

"He's my assistant. I don't ask anything of him that I can do myself.
But we're both Med Service. And I do things for him that he can't do for
himself. For example, I make coffee for him."

Murgatroyd heard the familiar word. He said;

"