s."

The creature had made itself at home aboard the _Mercy_. In the spirit
of uninvited guests since time immemorial, it had established a toehold
with remarkable asperity, and now was digging in for the long winter.
Drawn to the hydroponic tanks like a flea to a dog, the _hlorg_ had
settled its bulbous pink body down in their murky depths with a
contented gurgle. As it grew larger the tank-levels grew lower, the
broth clearer.

The fact that the twenty-five crewmen of the _Mercy_ depended on those
tanks for their food supply on the four-month run back to Hospital Earth
didn't seem to bother the _hlorg_ a bit. It just sank down wetly and
began to eat.

Under Jenkins' whip hand, and with Green Doctor Stone's assistance, the
Survey Crew snapped into action. Survey was the soul and lifeblood of
the medical services supplied by Hospital Earth to the inhabited planets
of the Galaxy. Centuries before, during the era of exploration, every
Earth ship had carried a rudimentary Survey Crew--a physiologist, a
biochemist, an immunologist, a physician--to determine the safety of
landings on unknown planets. Other races were more advanced in
technological and physical sciences, in sales or in merchandising--but
in the biological sciences men of Earth stood unexcelled in the Galaxy.
It was not surprising that their casual offerings of medical services
wherever their ships touched had led to a growing demand for those
services, until the first Medical Service Contract with Deneb III had
formalized the planetary specialty. Earth had become Hospital Earth,
physician to a Galaxy, surgeon to a thousand worlds, midwife to those
susceptible to midwifery and psychiatrist to those whose inner lives
zigged when their outer lives zagged.

In the early days it had been a haphazard arrangement; but gradually
distinct Services appeared to handle problems of medicine, surgery,
radiology, psychiatry and all the other functions of a well-appointed
medical service. Under the direction of the Black Service of Pathology,
Hospital ships and Survey ships were dispatched to serve as bases for
the tiny General Practice Patrol ships that answered the calls of the
planets under Contract.

But it was the Survey ships that did the basic dirty-work on any new
planet taken under Contract--outlining the physiological and biochemical
aspects of the races involved, studying their disease patterns, their
immunological types, their susceptibility to medical, sur