The mechanisms by which animals regulate the volume and composition of
their body fluids has long had a particular fascination for students of
biology. As a consequence, the subject can lay claim to an impressive
record of ground- breaking scientific achievements as well as a
provocative body of philosophical speculation concerning the role of the
system in the origin and evolution of life. Indeed, the entire concept
of homeostasis on which so much of o r current biologic thinking is
based, derives from Claude Bernard's pioneering exploration of the
forces that determine the composition of this 'internal sea'. Other
seminal achievements credited to this area of inquiry include the first
description of a genetically transmitted human disease (familial
neurogenic diabetes insipidus); the first isolation sequencing and
synthesis of a peptide hormone (vasopressin and oxytocin); the first
demonstration of peptide hormone synthesis by way of a larger protein
precursor; the first description of resistance to the biologic actions
of a hormone (nephrogenic diabetes insipidus); and the conceptual
realization of the unique counter-current mechanism that permits
concentration of the urine. This record of far reaching and fundamental
advances has been distinguished by many fruitful inter- actions between
clinical and basic science.