TRANSFUSION OF BLOOD 141 



Soon afterward, Belfanti and Carbone (July, 1898) dis- 

 covered the very important fact that the injection of rabbit 

 serum into a horse made the serum of this horse toxic for all 

 rabbits; and Bordet completed this experiment by showing 

 that the serum of any animal injected with the blood of an 

 animal of different kind, acquires the property of agglutinat- 

 ing and dissolving the red corpuscles and of forming a pre- 

 cipitate with the serum of the animal which furnished the 

 injected blood, on mixing both liquids in a test-tube. 



The reactions observed in vitro therefore allow us to per- 

 ceive what goes on in the organism, and to explain the 

 nature if not the fundamental mechanism of a series of 

 pathological reactions that might from this time on have led 

 us to regard immunity and the pathogenicity of certain 

 infectious diseases in a new light. 



The results of the experiments of Hayem, Behring and 

 Kitasato, Pfeiffer, Metchnikoff, J. Bordet, Kraus, Belfanti 

 and Carbone, and others, has been to emphasize the follow- 

 ing biological rules: 



1. The injection of a heterologous albumin (bacterial 

 bodies, blood, serum, casein, etc.) or of a non-albuminoid 

 bacterial product causes, in the injected organism, the forma- 

 tion of a substance in excess which possesses a specific 

 affinity for the injected substance. 



The name of "antibody" has been given to all the substances 

 thus formed, and of "antigen" to all those substances causing 

 such a formation. 



2. The antibodies neutralize in vitro and in vivo the specific 

 pathogenic action of the antigen toxin and of the infectious 

 antigen bacilli; but whereas the mixtures of antigen toxins 

 (non-albuminoid) with their antitoxins give a product which 

 is soluble "in vitro" and neutral in the organism the mix- 

 tures of the infectious antigen bacilli with their antibodies 

 give a product which forms a precipitate. This precipitate 

 is neutral from an infectious point of view in the case of 

 pathogenic bacilli, and from a toxic point of view for toxal- 

 bumins, but in itself it is endowed with a special toxicity. 



This special toxicity becomes evident when one eliminates 

 from the mixture the actual "toxin" or " infection" as for 



