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It is usually assumed that the fluctuations of the protein quotient under normal and pathological conditions are due directly or indirectly to variations in the general nature and especially in the rapidity of the metabolic processes. Thus, Cervello (1) ascribes to a retardation of metabolism the rise in globulins he obtained under the administration of antipyrin. Hurwitz and Meyer (2) suppose that the increase in the serum globulins in certain actue infections is due to metabolic disturbances. Schmidt and Schmidt (3) are inclined to believe that the serum proteins have no relation to immunity and would rather attribute the increase in globulins to changes in the metabolism resulting from the toxemia and tissue waste of acute infections. In view of the fact that alterations in the protein quotient have been so frequently attributed by various authors to disturbances in the metabolism, it was considered necessary to investigate the more precise relations of the globulin albumin ratio to difference in the rapidity of metabolism.

Summary A simple and accurate method of measuring the antitryptic indices of blood-sera is described. It is shown that for varying proportions of antitrypsin (= A) added to a specified amount of trypsin (regarded as unity) the relation: holds good for any given serum, T being the proportion of the trypsin neutralized by the serum and C a constant which is a direct measure of the number of molecules of antitrypsin contained in a specified volume of the serum. The molecular concentration of antitrypsin in blood serum is in great excess of the molecular concentration of proteolytically active material in a 1 per cent solution of Gruebler's trypsin.

Summary The normal variation in the antitryptic index is very marked in any particular rabbit, and is even greater in different animals. An unmistakable rise in the antitryptic index has been produced in at least two of the six rabbits immunized against trypsin. The progress of immune body production against trypsin is very peculiar, in that at first there is a marked fall in the antitrypsin, followed soon, however, by rather a sudden rise which is at best only 300 per cent above the normal variation. At this level the antibody content remains approximately stationary for a comparatively brief period and is then supervened by a rapid return to the normal, in spite of continued periodical injections of trypsin. Immunity to pancreas trypsin appears to cause no change in the protein quotient. This fact may serve as additional evidence in favor of the recently emphasized view that immunity is non-dependent on the concentration of the serum proteins.