172 CHEMISTRY OF THE IMMVSITY REACTIONS 



lated the animals the less sharply these reactions distinguish them, 

 until, with such closely related animals as dog and fox, or man and 

 apes, antisera for the blood of one react nearly as well with the 

 blood of the other, the existing differences being only quantitative. 

 The opinion therefore gained ground that the specificity depended 

 upon some peculiar biological relationship of the antigens, and, as 

 serum proteins which seemed to be quite similar chemically but which 

 were from unrelated species, were sharply differentiated by the bio- 

 logical reactions, that the specificity must depend upon something 

 quite distinct from ordinary chemical differences. But even with 

 closely related species, differences can often be brought out by means 

 of the process of saturation (which consists in treating the antiserum 

 with sufficient quantities of an antigen until it no longer reacts with 

 additional quantities of this antigen, and then trying its reactive 

 power with the other related antigen which one wishes to test). 



As use began to be made of other materials than serum, and 

 especially when more or less purified proteins were employed, it was 

 found that within the tissues of a single animal or plant there might 

 exist antigens which were quite distinct from one another — more so, 

 indeed, than some of the chemically similar substances of different 

 biological origins. Thus, in the hen's egg, by means of the anaph}'- 

 laxis reaction, I have been able to distinguish five distinct antigens, 

 and these correspond to as many different proteins which have been 

 distinguished by chemical means. ^'' Also, for another example, in 

 the crystalline lens are found proteins which are specific for lens 

 proteins, in that they produce antibodies reacting with lens proteins 

 from varied species of animals, but not with the serum proteins of 

 the species from which the antigenic lens substance was derived.*" 

 Here the chemical character of the protein is undoubtedly more 

 ^significant than its biological relations. These and other observa- 

 tions leave little room for doubt that specificity does depend upon 

 chemical composition, and that the differences in species as exhibited 

 hy their biological reactions depend iipon distinct differences in the 

 chemistry of their proteins.*°'^ Chemically distinct proteins {e. g. lens 

 and serum proteins) of one animal may be immunologically distinct, 

 and chemically related proteins of dissimilar species (c. g. casein 

 from goat and cow milk) may shoAV immunological relationship. 

 Crystalline albumin from hen's eggs shows no immunological distinc- 

 tion fi-om that of ducks' eggs, whereas eacli of the three ju'oteins sep- 

 arable fi'om horse serum — euglobulin, pseudoglobulin and albumin — 

 can l)e distinguished from the other two l)y the anaphylaxis reac- 

 tion.''"'' Furthermore, it h.as been shown by AVells and Osborne *^ 



30 Jour. Infeo. Dis., 1911 (9), 147. 



40 Spc Knisiua, Zcit. Immunitiit., 1910 (5), tlOi). 



40ii8ee WoUs and Oaboriic, Jour. Infect. Dis.. 1910 (19), 183. 



•if'hDalc and Ilardov, Hiocliem. Jour., 191G (10), 408. 



■ii.ldwr. Infect. Dis.", 191.3 (12), 341. 



