INTRODUCTION 



Up to the present time investigations on immunity have been 

 directed toward solving the following question: What are the 

 means of defense which permit an immunized animal or one 

 naturally refractory to resist infection? These studies have 

 resulted in the development of diverse theories. 



When an animal is affected with a contagious disease of bac- 

 terial origin, the cellular immunity, which we call "organic 

 immunity," abstracting it from all theory as to its intimate na- 

 ture, is only established in a variable length of time after the 

 inception of the disease. Does the animal remain without de- 

 fense up to the time that this organic immunity becomes effec- 

 tive? By what phenomenon is it possible to acquire this organic 

 immunity? 



All animals sensitive to an infection and exposed to it do not 

 contract the disease. Why do some of them remain unharmed? 



These are the principal points upon which the experiments to 

 be discussed have turned. As will be seen, they lead to a new 

 chapter in the study of the means of defense against infection; 

 and the conclusions themselves which will be derived from these 

 investigations will not actually contradict anything in the present 

 theories, for they apply to different states. 



There is, nevertheless, a particular point in the present theories 

 of immunity to which I wish to call attention, namely, that which 

 deals with bacteriolysis as induced by specific sera. This is 

 certainly pertinent since it deals with the subject under dis- 

 cussion: the lysis of bacteria. 



Everyone knows the nature of the phenomenon of Pfeiffer. If 

 one injects a suspension of cholera vibrios into the peritoneal 

 cavity of a guinea pig previously "immunized," a transformation 

 of these vibrios into granules is noted. Pfeiffer has suggested 

 that the transformation into granules constitutes only the first 

 phase of the vibriolysis; but in this he was in error, for the granules 

 maintain this form indefinitely. 



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