[48] Richet, C., _L'anaphylaxie_. Paris, 1912.
[49] Quoted from Wells, H. G., _Jour. Infect. Diseases_, 1908, v., 449.
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.
He considered this a case of a real synthesis of proteins from the products of its hydrolytic cleavage. This interpretation was not generally accepted and received a different interpretation by Bayliss and other workers. Gay and Robertson were able to show that paranuclein when injected into an animal will sensitize guinea-pigs for anaphylactic intoxication for either paranuclein or casein and apparently indiscriminately. The products of complete peptic digestion of casein had no such effect, but the synthetic product of this digestion obtained by Robertson's method has the same specific antigenic properties as paranuclein, thus making it appear that Robertson had indeed succeeded in causing a synthesis of paranuclein with the aid of pepsin from the products of digestion of casein by pepsin.
There are a few statements in the literature to the effect that the specificity of organisms might be due to other substances than proteins. Thus Bang and Forssmann claimed that the substances (antigens) responsible for the production of hemolysis were of a lipoid nature, but their statements have not been confirmed, and Fitzgerald and Leathes[52] reached the conclusion that lipoids are non-antigenic. Ford claims to have obtained proof that a glucoside contained in the poisonous mushroom _Amanita phalloides_ can act as an antigen. But aside from this one fact we know that proteins and only proteins can act as antigens and are therefore the bearers of the specificity of living organisms.
[52] Fitzgerald, J. G., and Leathes, J. B., _Univ. Cal. Pub._, 1912, "Pathology," ii., 39.
Bradley and Sansum[53] found that guinea-pigs sensitized to beef or dog hemoglobin fail to react or react but slightly to hemoglobin of other origin. The hemoglobins tried were dog, beef, cat, rabbit, rat, turtle, pig, horse, calf, goat, sheep, pigeon, chicken, and man.