Chapter J 



The Demonstration of Individuality Differentials 



by Serological Methods 



IN the preceding chapter we have discussed various investigations which 

 tended to prove the existence of species, generic and class differentials 

 by means of serological methods. We have seen that the precipitin test 

 in general permits only the distinction of relatively far distant species, but 

 certain refinements in technique may make it possible to distinguish also be- 

 tween more nearly related species. At an early period of these investigations, 

 it was especially Hamburger who suggested that not only species differed in 

 their chemical constitution, but that also individuals might differ. It was 

 therefore natural that the attempt should be made to demonstrate differences 

 between the proteins of different individuals by means of methods similar to 

 those used for the demonstration of species differentials. Weichardt seems to 

 have been the first to make experiments of this kind. He believed that he was 

 able to demonstrate individual differences in the degree of precipitation taking 

 place on mixing the blood proteins of two individuals with their respective 

 antisera, after previous saturation of the antiserum of one with the serum of 

 the other individual. The sera then appeared to react more strongly with the 

 individual antigen used for immunization. Weichardt used heterogenous im- 

 mune bodies in his investigations and in the light of what we have since 

 learned concerning the limitations of the precipitin test, it is very improbable 

 that individuality differentials can be demonstrated by these means. 



However, a few years previous to this work Ehrlich and Morgenroth, 

 using a different technique, had actually shown the existence of individual 

 differences between antigens, in experiments to which we have referred 

 already. But it seems that these investigators were not primarily interested in 

 the analysis of what we now would designate as individuality differentials; 

 they wished, rather, to determine whether immune substances could be pro- 

 duced only against heterogenous substances, and whether a condition which 

 Ehrlich had named "Horror autotoxicus" would prevent the formation of 

 antibodies in an animal of the same species. They therefore injected massive 

 doses of hemolyzed blood corpuscles of thirteen goats into other goats and 

 obtained thirteen hemolysins for the blood corpuscles of the individuals which 

 had served as donors of the antigens. A comparison of the effects of the 

 different immune sera on the blood corpuscles of the various individuals 

 showed that the sera were not all alike, but that each one behaved in a dis- 

 tinctive manner. It could furthermore be shown that the differences depended 

 not only on the kind of corpuscles injected, but also on the animal which had 

 produced the hemolysins. Thus two different goats, injected with the same 

 goat blood, gave different hemolysins. This corresponds with the results 



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