HISTORY OF THERAPEUTICS 23 



10. THE CHEMOTHERAPY OF EHRLICH 



Definition of Chemotherapy. — Formerly, the pharmacology of 

 medicines was tested only on healthy animals, and only drugs which 

 produced symptomatic effects were included in the tests. Medi- 

 cines which act specifically were tested rarely (quinine against 

 malaria, mercury and iodine against syphilis). The new experi- 

 mental therapeutics produces certain infectious diseases artificially 

 in experimental animals and studies the action of curative agents 

 upon these diseased animals. Specific medicines are also produced 

 Bjmthetically for use in the treatment of certain infectious diseases. 



Ehrlich has shown experimentally that the specific relations of 

 the curative agent to different parts of the body, its so-called tropic 

 properties, may be very different. A distinction must be made 

 between the organotropic action, i.e., the relation to certain organs 

 (neurotropic action, etc.), and the parasitotropic action, which is 

 exerted not upon the animal body itself but upon the parasites 

 present in the body. In serum therapy, products of the body act 

 as protective agents in a purely parasitotropic manner and without 

 any organotropic effect. Since the body and its cells are not influ- 

 enced by these protective substances, serum therapy excels any 

 other method of treatment in those cases to which it is applicable. 

 But serum therapy cannot be employed in some of the infectious 

 diseases, e.g., in malaria, trypanosomiasis, and spirillosis. In such 

 cases, chemical antiparasitic remedies must be used (chemotherapy 

 instead of serum therapy). These chemical substances, however, 

 are mostly poisons, which are not only harmful to the parasites 

 but also to the organism (parasitotropic and organotropic action). 

 In chemotherapy, only such medicines can be used as will kill the 

 parasites without doing any considerable harm to the body. Cor- 

 rosive sublimate, carbolic acid, and arsenic are not suitable on 

 accoimt of their strong organotropic action. On the other hand, 

 the extremely poisonous organotropic action of arsenic can be re- 

 duced by certain synthetical combinations and the parasitotropic 

 action relatively increased. The first of these synthetic, chemo- 

 therapeutic, arsenical preparations were atoxyl (sodium arsanil- 



