This book traces the development of the kidney from amoeba to man, through all its intermediary stages among the early forms of life, lungfish, reptiles, birds and mammals. It equates the changes in this organ with the changes in the geologic development of the world, and has in fact a wide philosophic and scientific perspective- and Dr. Smith brings an almost rhapsodic appreciation to his study of this particular internal organ. And he takes his theme from the words of Claude Bernard- a hundred years ago- ""the true medium in which we live is neither air nor water, but the plasma or liquid part of the blood that bathes all the tissue elements"". In other words, our internal environment. Dr. Smith, a Professor of Physiology at the N.Y.U. School of Medicine, is also the author of Man And His Gods and a very serious scholar and interpreter. But one questions whether the general public will share his ecstatic enthusiasm for the role the kidney has played in his prehistoric past and current present.