1. In the minor surgical cases (considered normal) the chemical composition of the blood serum agrees, as far as its proteins are concerned, with the usual standard values. When examined at different times, the serum of such cases shows no variation in the total protein content or in its individual fractions. The incoagulable nitrogen, however, varies considerably in the total amount in the different cases, as well as in its percentage relations to the other constituents of the serum.

2. The cases of prostatic hypertrophy, with or without chronic interstitial nephritis, show no change from the normal in the character of the protein composition of the serum, nor in the ratio which the individual fractions bear to each other. On the other hand, the incoagulable and non-protein nitrogen of the serum show marked fluctuations, some of which correspond to the degree of functional deficiency of the kidneys.

3. In cases of localized infections of the kidneys, the changes in the blood serum are twofold. One concerns the proteins, and is traceable to the infection; and the other concerns the non-protein nitrogen, results from functional impairment, and varies with the amount of destruction of the kidney substance. Thus an increase in the globulins is observed in these sera similar to that occurring in infections in other localities; the non-protein content increases apparently in direct proportion to the degree of deficiency of the kidney, and becomes diminished when the function of the kidneys improves.