There can be no doubt that on the basis of our present knowledge proteins are in most or practically all cases the bearers of this specificity. This has been found out not only with the aid of the precipitin reaction but also with the anaphylaxis reaction, by which, as the reader may know, is meant that when a small dose of a foreign substance is introduced into an animal a hypersensitiveness develops after a number of days or weeks, so that a new injection of the same substance produces serious and in some cases fatal effects. This hypersensitiveness, which was first analysed by Richet,[48] is specific for the substance which has been injected. Now all these specific reactions, the precipitin reaction as well as the anaphylactic reaction, can be called forth by proteins. Thus Richet, in his earliest experiments, showed that only the protein-containing part of the extract of actinians, by which he called forth anaphylaxis, was able to produce this phenomenon, and later he showed that it was generally impossible to produce anything resembling anaphylaxis by non-protein substances, _e. g._, cocain or apomorphin.[49] Wells isolated from egg-white four different proteins (three coagulable proteins and one non-coagulable) which can be distinguished from each other by the anaphylaxis reaction, although all come from the same biological object.[50] Michaelis as well as Wells found that the split products of the protein molecule are no longer able to call forth the anaphylaxis reaction. Since peptic digestion has the effect of annihilating the power of proteins to call forth anaphylaxis, we are forced to the conclusion that the first cleavage products of proteins have already lost the power of calling forth immunity reactions. [48] Richet, C., _L’anaphylaxie_. Paris, 1912. [49] Quoted from Wells, H. G., _Jour. Infect. Diseases_, 1908, v., 449. [50] _Ibid._, 1911, ix., 147. A pretty experiment by Gay and Robertson[51] should be mentioned in this connection. Robertson had shown that a substance closely resembling paranucleins both in its properties and its C, H, and N content can be formed from the filtered products of the complete peptic hydrolysis of an approximately four per cent. neutral solution of potassium caseinate by the action of pure pepsin at 36°C. [51] Gay, F. P., and Robertson, T. B., _Jour. Biol. Chem._, 1912, xii., 233.