470 BACTERIOLOGY. 



ulence is due to a gradual tolerance acquired by the 

 cells of the tissues to the action of the poison when 

 produced in these small quantities; in the same way 

 that a tolerance was acquired by the tissues for the 

 venom of the rattlesnake in the experiments of Sewall 1 

 (and more recently in the work of Fraser, Calmette, 

 Weir Mitchell, and others), and similar to that follow- 

 ing the injection into the tissues of small quantities of 

 hemialbumose, which in large amounts rapidly proves 

 fatal. 



Of utmost importance to these studies of the blood 

 and fluids of the body are the experiments of Behring 

 and Kitasato 2 upon the production of immunity to teta- 

 nus. In their investigations upon the blood of animals 

 subjected to these experiments it was found that it was 

 not only possible to render animals immune from this 

 disease, but that the serum of the blood of these immu- 

 nized animals afforded immunity when injected into the 

 peritoneal cavity of other animals that had not been so 

 protected; and moreover, that this serum possesses cura- 

 tive powers over the disease after it has, in some cases, 

 been in progress for a time. They found, further, that 

 the serum of animals that had been rendered immune 

 from tetanus, when brought in contact with the poison of 

 tetanus, completely destroyed its poisonous properties, 

 and that the serum from animals or from human beings 

 that do not possess immunity from this disease has no 

 such power. 



The demonstration by Behring and Kitasato of the 

 fact that the serum of an immunized animal can not 

 only confer immunity to another susceptible animal, 



1 Journal of Physiology, 1887, vol. \ii. p. 203. 



2 Behring and Kitasato; Peutsche med. Woch.. 1890. Bd. xvi. p. 1113. 



