PHENOMENA FOLLOWING IMMUNIZATION 99 



and that this is a definite indication that the antigen in one case must 

 be chemically different from that in another. 



The range of such variations is apparently enormous. For each 

 variety of bacteria or plant, each species of animal, and to a certain 

 extent each individual of the species, possesses certain special anti- 

 genie characteristics peculiar to itself. In general there is an under- 

 lying antigenic similarity which is peculiar to the species. This is 

 true of bacteria and, in the case of animal and vegetable proteins, an 

 antibody produced with material from an individual of a certain 

 species will react with the protein derived from this species in gen- 

 eral. However, that there are also antigenic differences between in- 

 dividuals within the same species is indicated by Ehrlich's experi- 

 ments on the antibodies produced by injecting the blood cells of one 

 goat into another. And we have further indicated that within the 

 same animal different organs may possess individual antigenic char- 

 acteristics. Added to this we know that certain special organs like 

 the testicle, the lens, and some others contain antigens which are 

 peculiar to this variety of organ, irrespective of species a condition 

 spoken of as "organ specificity/' Thus an antibody produced by 

 injections of the testicular substance of one animal will react with 

 testicular protein from many different species the specificity here 

 depending upon the organ and not upon the zoological relationship. 



It is clear, therefore, that there are more different varieties of 

 protein, biologically distinguishable, than there are species of living 

 beings in nature. As Abderhalden 74 has recently pointed out, this 

 is a conception which it is a little difficult to grasp chemically, since 

 in breaking up different proteins into their "building stones" (Bau- 

 steine) we encounter again and again the same 20 amino-acids. By 

 a simple arithmetical consideration, however, he shows that merely 

 by combining these twenty amino-acids in different groupings an 

 enormous number of isomeric but varying compounds can be formed 

 even without assuming the additional possibility of quantitative 

 variations. He reasons that 3 "Bausteine" A, B, and C could 

 form 6 different structures, A B C, A C B, B C A, B A C, C A B, 

 C B A. Similarly 4 could form 26, and finally 20 could form 2, 432, 

 902, 008, 176, 640, 000 different compounds. 75 



The analogy between the active immunization of animals with 

 the various antigens and certain chemically well-defined poisons, 

 alkaloids, etc., is so obvious that it has led to much speculation as to 

 a possible similarity in the physiological mechanisms of the two phe- 

 nomena. As a matter of fact the acquired tolerance for such sub- 

 stances as morphin, atropin, and other alkaloids is not really anal- 

 ogous to the physiological reactions which follow the treatment of an- 



74 Abderhalden. Munch, med. Woch., No.' 43, 1913. 



75 We have not repeated the arithmetical labor and take Abderhalden's 

 word for it. 



