XII. THE PRINCIPLES UNDERLYING THE 



TREATMENT OF SYPHILIS WITH 



SALVARSAN (" 606 ") 



As a result of some of his earliest researches and 

 in entire accordance with his views as already set 

 forth under "Antitoxins," Ehrlich has always held 

 that the action of a chemical substance on a given 

 cell denotes the existence of definite chemical affini- 

 ties between the substance and the cell. Applying 

 this conception to the germicidal action of chem- 

 icals, he maintains that the latter must have a 

 certain chemical affinity for the parasites in order 

 to kill them. Substances having such affinities 

 he terms " parasitotropic." It is clear, however, 

 that substances which can destroy parasites will 

 also be poisonous for the animal body, i.e., they 

 will have chemical affinity for the vital organs of 

 the host. They are, therefore, also " organotropic." 

 In the employment of chemical substances in com- 

 bating infectious diseases it follows that success 

 can only be attained if their chemical affinity for 

 the infecting parasite bears certain relations to their 



affinity for the infected body. 



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