"_Blueskin: Colloquial term for a person recovered from a plague
which left large patches of blue pigment irregularly distributed
over the body. Especially, inhabitants of Dara. The condition is
said to be caused by a chronic, nonfatal form of Dara plague and
has been said to be noninfectious, though this is not certain. The
etiology of Dara plague has not been worked out. The blueskin
condition is hereditary but not a genetic modification, as markings
appear in non-Mendelian distributions_."

Calhoun puzzled over it. Nobody could have read the entire Sector
directory, even with unlimited leisure during travel between solar
systems. Calhoun hadn't tried. But now he went laboriously through
indices and cross-references while the ship continued to travel
onward.

He found no other reference to blueskins. He looked up Dara. It was
listed as an inhabited planet, some four hundred years colonized, with
a landing-grid and, at the time the main notice was written out, a
flourishing interstellar commerce. But there was a memo, evidently
added to the entry in some change of editions: "_Since plague, special
license from Med Service is required for landing._"

That was all. Absolutely all.

The communicator said suavely:

"Med Ship _Aesclipus Twenty_! Come in on vision, please!"

Calhoun went to the control board and threw on vision.