DEMONSTRATION OF SPECIES DIFFERENTIALS 507 



against the erythrocytes — and presumably also against other cells — of a 

 certain species. Thus specificities, if they exist, may be obscured by the ex- 

 istence of a multiplicity of preformed antibodies which may interfere with 

 one another. Accordingly, Landsteiner and Levine found, as stated above, 

 that a serum after absorption with chimpanzee erythrocytes, acted much less 

 on chimpanzee than on human blood, and the converse effect was seen after 

 absorption with human blood cells. Also, in other instances when sera and 

 cells of sheep, goat, fox and dog were used, it has been possible through 

 absorption with erythrocytes, or in some cases, with other cells of a certain 

 species, to remove from a serum, in a specific way, the agglutinins acting on 

 the cells of this species, while leaving behind the agglutinins for the erythro- 

 cytes of another species. In some instances however, this absorption did not 

 act in such a specific manner, but with the specific agglutinins for the cells 

 of one species there were removed also those acting on the cells of a different 

 species. 



Furthermore, when once a definite threshold of strangeness has been 

 reached, a finer differentiation among the strange species, as to the degree of 

 toxicity of substances present in their sera or cells, will hardly be possible. 

 This applies as far as preformed substances in sera and cells are concerned, 

 but not in the case of immune sera. In a similar way, we found that in 

 heterotransplantation the conditions existing in the host are so intensely in- 

 jurious for the transplant that finer gradations in the degree of injuriousness 

 of different species, in accordance with the systematic relationship between 

 host and transplant, are very difficult or even impossible to accomplish. 



As to the effects of the injection of foreign sera into the circulation of 

 rabbits, we noticed that these animals succumb readily when a certain amount 

 of the heterogenous serum has been injected with a given rapidity. But again, 

 different factors may be responsible for such a fatal outcome in the case of 

 sera from different species and this diversity of factors precludes a strict 

 parallelism between the systematic relationship of the various species used 

 and the toxicity of their sera. Thus, according to Strickler, Tuttle and Loeb, 

 intravenous injection of dog serum kills the rabbit, essentially, by the hemoly- 

 sis it produces in the blood vessels of the rabbit. The products of hemolysis 

 cause coagulation of the blood in the living animal in the same way as in 

 vitro. Accordingly, the pulmonary vessels and the vena cava become filled 

 with blood clots and the animal dies from asphyxiation. If the formation of 

 blood clots is prevented by injection of hirudin or heparin into a vein previous 

 to the injection of the serum, the latter does not kill the rabbit. The heparin 

 diminishes hemolysis as well as the coagulation of the blood (Rabinovitch). 

 Beef serum, on the other hand, causes, in vitro as well as in vivo, agglutination 

 of the erythrocytes ; the clumps of red corpuscles formed occlude the pulmo- 

 nary vessels and death results. Directly after the death of the animal these 

 agglutination thrombi may be demonstrated by exerting pressure on the 

 pulmonary vessels, which forces the thrombi out of the cut vessels (Rabin- 

 ovitch). It is possible that in addition to these toxic effects of dog and beef 

 serum, other factors are involved in some instances; thus Zinsser maintains 



