INFECTION AND IMMUNITY. 471 



but in the case of tetanus (and diphtheria, as subse- 

 quently demonstrated by Behring and his associates), 

 cure the disease after it is already in progress, is one of 

 the most important steps that has been made in this 

 entire field of study. The subsequent application of the 

 principle involved in that observation by Behring and 

 his colleagues, in their successful efforts to devise a cure 

 for diphtheria in man, has resulted in a triumph which 

 marks an epoch in modern scientific medicine. The 

 same principle has been employed for obtaining cura- 

 ative agents against other forms of infection and intoxi- 

 cation, notably, of Asiatic cholera, typhoid fever, lobar 

 pneumonia, streptococcus and staphylococcus infection, 

 rabies, tuberculosis, bubonic plague, syphilis, vaccinia, 

 and serpent venom; but unfortunately, as yet, with but 

 indifferent success ; certainly in no case to the same 

 favorable degree as has been seen in the treatment of 

 diphtheria with antitoxic serum. 



Another hypothesis in explanation of the immunity 

 acquired by the tissues of the animal organism is that 

 advanced by Buchner, 1 who suggests that in the primary 

 infection, from which the animal has recovered, there 

 has been produced a reactive change in the integral cells 

 of the body that enables them to protect themselves 

 against subsequent inroads of the same organism. 

 Though somewhat more vague at first glance than the 

 other theories in regard to this phenomenon, it is, never- 

 theless, in the light of subsequent research, most prob- 

 ably the correct explanation of the establishment of 

 immunity in many, if not all, cases. Experiments that 

 bear directly upon this idea have demonstrated that, if 



1 Buchner : Eine neue Theorie liber Erzielung von Immunitat gegen In- 

 fektionskrankheiten. Miinchen, 1883. 



