16 MODERN BIOLOGIC THERAPEUSIS 



ing a more complete understanding of immunity 

 against living microorganisms, and of measur- 

 ing this immunity by the opsonic index. 



In America, bacteriology and pathology have 

 been advanced by William H. Welch (1850-), 

 while Theobald Smith (1859-) has been one of 

 the pioneers in the theories of infectious dis- 

 eases. In 1885 Smith carried out immunizing 

 experiments in connection with his studies of 

 American diseases of hogs. His work along 

 this line constitutes the first experiments in 

 immunization and was soon followed by the 

 work of von Behring, Roux and others in human 

 medicine. 



Immune Therapy About 1890 Pasteur's the- 

 ory of attenuated viruses was extended to the 

 science of toxins and antitoxins by von Behring 

 (1854-). While working in Koch's Institute 

 with Kitasato, von Behring demonstrated that 

 the serum of animals immunized against diph- 

 theria toxin can be used as a preventive or ther- 

 apeutic inoculation against diphtheria in other 

 animals through a specific neutralization of the 

 toxin of the disease. After trying out the rem- 

 edy in man, von Behring began to produce it 

 upon a grand scale (1894) and it soon became 



