166 CHEMISTRY OF THE IMMUNITY REACTIONS 



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 specificitj' depends upon some 

 peculiar biological relationship of the antigens, and, as serum proteins 

 which seem to be quite similar chemically but which are from un- 

 related species, are sharply differentiated by the biological reactions, 

 that the specificity must depend upon something quite distinct from 

 ordinar}' chemical differences. But even with closely related species, 

 differences can often be brought out by means of the process of satura- 

 tion (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 anaphy- 

 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 

 by their biological reactions depend upon distinct differences in the chemis- 

 try of their proteins.^^ Chemically distinct proteins (e. g. lens and serum 

 proteins) of one animal may be immunological!}' distinct, and chemically 

 related proteins of dissimilar species (e. g. casein from goat and cow 

 milk) may show immunological relationship. Crystalline albumin 

 from hen's eggs shows no immunological distinction from that of ducks' 

 eggs, whereas each of the three proteins separable from horse serum — 

 euglobulin, pseudoglobulin and albumin — can be distinguished from 

 the other two by the anaphylaxis reaction. "^^ Furthermore, it has 

 been shown by Wells and Osborne*'^ that a single pure protein may 

 exhibit multiple antigenic properties, and react or fail to react with 



" Jour. Infec. Dis., 1911 (9), 147. 



•" Krusius, Zeit. Irinimnit:it., 1910 (.5), r)99. 



"See Wells and ()sl)<)ni(-, Jour. Infect. Dis., 19H) (19), 183. 



" Dale and IfarUcy, liioclieni. Jour., 191C. (10), 40S. 



"Jour. Infect. Di.s., 1913 (12), .341 



