534 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



intensified in certain instances. Serologically, organ differentials have been 

 tested in vitro mainly by means of the precipitin or complement fixation 

 reactions ; organ differentials have also been tested in the living animal by 

 means of specific cytotoxic effects following injection of immune serum 

 against a certain organ, or by means of anaphylactic reactions. 



In the large majority of cases where an organ differential has been shown 

 to exist, the simultaneous presence of the organismal differential in the 

 material serving as antigen could likewise be established, or at least made 

 probable. A combination of these two antigens is indicated under the 

 following conditions : 



a. If an immune serum reacts not only with the organ or the substance 

 used as antigen, but also with other organs or fluids of the same species, 

 although to a lesser degree, this might be due to the presence of an organismal 

 differential in the antigen; but, as stated above, this is not necessarily the 

 case. 



b. The conclusion that also an organismal differential is involved in the 

 reaction is strengthened if the immune serum reacts with the analogous 

 organs of other species in such a way that the reaction is the more intense, 

 the nearer the species providing the antigen and the second species to be 

 tested are related to each other. 



c. If the immune serum reacts only with the organ of the donor species 

 which served as antigen, but not with other organs or with the blood of the 

 donor species, and if it does not react with the analogous organs of other 

 species, then such an immune serum may or may not be directed also against 

 the organismal differential. We may possibly have to deal with an immune 

 serum specific for a certain substance which does not possess an organismal 

 differential. But if the immune serum, while reacting most intensely with the 

 antigenic organ of the donor species, reacts likewise, although more weakly, 

 with other organs of the same species, but does not react with the correspond- 

 ing organs of other species, then the material which served as antigen contains 

 in all probability both organ and organismal differentials. The lack of a 

 reaction with any other species in such a case may represent the end-stage 

 in a series of reactions, in which the intensity of the reaction decreases more 

 and more with the increasing distance in relationship between the antigen- 

 providing species and the other species which are to be compared with the 

 former. 



Various organs, and substances derived from these organs, differ very 

 much as to the degree of their organ- and substance-specificity. According 

 to Fleisher, who used in vitro tests, the simultaneous presence of species- 

 specific substances and of substances of a non-specific character in various 

 organs complicates the demonstration of the organ- and tissue-specific sub- 

 stances which they contain. But quite apart from these complications, different 

 organs actually seem to vary considerably in the readiness with which 

 these organ-specific substances can be demonstrated. Thus, Fleisher states 

 that it is very difficult to demonstrate them in the spleen, but that this can be 

 more easily done in liver and kidney. We have referred to the marked 



