INFECTION AND IMMUNITY. 655 



The demonstration by Behring and Kitasato of the 

 fact that the serum of an immunized animal can not 

 only confer immunity upon another susceptible animal, 

 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 application of the principle 

 involved in this observation to the care of diphtheria 

 in man has resulted in a triumph which marks an epoch 

 in modern scientific medicine. The same principle has 

 been employed for obtaining curative agents against 

 other forms of infection and intoxication, notably, of 

 Asiatic cholera, typhoid fever, lobar pneumonia, strep- 

 tococcus and staphylococcus infection, rabies, tuberculosis, 

 bubonic plague, syphilis, vaccinia, and serpent-venom ; 

 but unfortunately, as yet, with only 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,^ 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 has, 

 nevertheless, much to recommend it, and in the light 

 of subsequent research is regarded by many as prob- 



1 Buclmer : Eine neue Theorie uber Erzielung von Immunitat gegeu 

 Jnfetstionskrankheiten. Muenchen, 1883, 



