Star Surgeon by Alan Edward Nourse

It was a long way from the students' barracks to the pathology sector where Black Doctor Arnquist lived. Dal Timgar decided not to try to go to the barracks first. It was after midnight, and even though the message had said "regardless of hour," Dal shrank from the thought of awakening a physician of the Black Service at two o'clock in the morning. He was already later arriving at Hospital Seattle than he had expected to be, and quite possibly Black Doctor Arnquist would be retiring. It seemed better to go there without delay.

But one thing took priority. He found a quiet spot in the waiting room near the subway entrance and dug into his day pack for the pressed biscuit and the canister of water he had there. He broke off a piece of the biscuit and held it up for Fuzzy to see.