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THE AMERICAN NATURALIST [Vol. LV 



of hybrid-stocks in plants— such facts taken all together 

 are gradually constructing for the biologist a rational 

 biochemic basis for the study of the fundamental proc- 

 esses operative in metabolism, heredity and evolution. 



But let us now turn our attention to another type of 

 serological reactions, those concerned with the cytotoxins 

 or cytolysins. You doubtless all recall the well-known 

 experiments of Bordet, in 1898, in w4iich he found that 

 the blood of guinea-pigs which have been repeatedly in- 

 jected with the red blood corpuscles of the rabbit, acquire 

 the property of rapidly dissolving rabbit corpuscles. 

 This is the familiar phenomenon of hemolysis, and the 

 substance in the blood-serum of the guinea-pig which 

 brings about solution of the red corpuscles of the rabbit 

 is termed a hemolysin. Bordet showed further that this 

 enhanced solvent action of the serum of animals treated 

 with the red blood cells of a different species exists only 

 for the kind of red corpuscles used as antigen, not for 

 those of other species of animals. Exceptions occur, 

 though in the main the reaction is specific. The similar 

 facts regarding bacteriolysins, which are now, common- 

 places of every-day medicine, had been established a 

 year earlier. 



It was soon discovered that other materials such as 

 leucocytes, nervous tissue, spermatozoa and crystalline 

 lens, when injected into the blood of a foreign species 

 will form lytic or toxic substances more or less specific 

 for the antigen used in the immunizing process. While 

 it is probable that none of such cytotoxins or cytolysins 

 acts only upon its o^\ti antigen— all studied so far have 

 been found to be somewhat hemolytic— the important 

 fact, for our present purposes, is that although a par- 

 ticular cytolytic -serum may affect some other tissues, it 

 vigorously attacks the special tissue used as antigen. 



This fact, when fully grasped, suggests inevitably to 

 the biologist, or at least to the investigator interested in 

 the mechanism of heredity and variation, queries such as 

 the following : if a special serum can thus be constructed 



