Man is born with at least twice as much kidney tissue as he requires. This fact is proved by the health of numerous persons who have sustained unilateral nephrectomy. Probably this wide margin of safety in the matter of surplus kidney substance has intimate relation to the difficulty of diagnosis of renal disease in its earlier or milder stages. So far as meeting the necessary demands for excretion it would seem to be an indifferent matter whether one kidney be removed or half the elements of each kidney be destroyed by disease.
For the purpose of the present study we are ignoring certain important features of nephritis, namely, evidence that the disease is constitutional rather than confined to an organ; that its tendency seems progressive; that connective tissue growth in healing within an organ produces of itself an extension of destruction of organic elements. But in the early stages of