i2 4 THE POPULAR SCIENCE MONTHLY 



them, as also to Ricketts, who investigated Mexican typhus and suc- 

 cumbed to it, and to Walter Myers and Everett Dutton, of the Liverpool 

 School, our science owes much in methods and in ideals. 



Truly, no field of medicine offers so much of tragedy, of romance 

 and of spectacular discovery as that of the pathogenic protozoa, and 

 few offer such great difficulties. It is, however, one of the most 

 promising fields of present-day effort and one which I would like to 

 present more in detail. It must, however, suffice to end this presen- 

 tation with mere mention of the successful cultivation of amebse 

 (Mesnil and Mouton), the cultivation of the trypanosomes (Novy and 

 MacNeal), the discovery by Schaudinn and Hoffman of the spirochete, 

 which we now know to be the cause of syphilis, and the finding of a 

 very similar organism in yaws. Time might also be given to the 

 various trypanosomes, to the spirochetes causing diseases of cattle 

 and poultry and to the Negri bodies of rabies; also the discussion 

 might be extended to include the broader field of tropical medicine, 

 but instead, as it is the direct outcome of the study of protozoa, I 

 must turn to a new phase of research in medicine, that known as 

 chemotherapy. 



Chemotherapy 



As the study of protozoan diseases progressed it soon became evi- 

 dent that the method of combating such diseases must be different from 

 that used against diseases due to bacteria. The chronicity of amebic 

 dysentery and relapses in malaria indicated that the protozoan diseases 

 are not self-limited and therefore not characterized by the development 

 of immune bodies, similar to those of the acute bacterial diseases; also 

 artificial cultivation failed to demonstrate that protozoa yielded bodies 

 analogous to bacterial toxins, capable of producing, on injection, bodies 

 with efficient antitoxic power. These and other facts precluded, there- 

 fore, a therapy based on the principles applied to bacterial vaccines or 

 antitoxins. 



The beneficial effect of quinine in the treatment of malaria and the 

 cellucidal action of quinine on the ameba and other protozoan forms 

 indicated that a therapy, to be successful, must be one in which a sub- 

 stance toxic for the protozoa in question is brought into direct contact 

 with it. The establishment of such therapy and incidentally the crea- 

 tion of a new science, that of specific chemical therapeutics, has 

 been the work, in the past seven years of Professor Ehrlich, of the 

 Royal Prussian Institution for Experimental Therapeutics at Frank- 

 furt. This new therapy is based on the principle that " a specific 

 chemical affinity exists between specific living cells and specific chem- 

 ical substances." This principle has always been the main theme of 

 Ehrlich's work, as is seen in his application of the aniline dyes to the 



