RESEARCH IN MEDICINE 125 



study of the cells of the blood, his studies on vital staining and the 

 selective action of methylene blue on the nervous system, the use of 

 methylene blue in the study of the oxidations and reductions occurring 

 in tissues, and his extensive studies in immunity. This experience, 

 covering a period of twenty-five years, led Ehrlich to the belief that 

 " for each specific parasite a specific curative drug must and could be 

 found." And upon this assumption he began his experiments. 



To appreciate thoroughly the difficulties of this task and the magni- 

 tude of the results, it must be understood that Ehrlich proposed a 

 sterilization of the body in so far as the microorganism, against which 

 the specific remedy was aimed, was concerned. The destruction of 

 bacteria or protozoa outside the body by chemical means is a common- 

 place of surgical and public health measures; but the destruction of 

 living microorganisms within the living body had never, until Ehrlich 

 accomplished it, been possible without, at the same time, destroying 

 also, in part or in toto, the cells of the host. To avoid the latter it 

 was necessary, therefore, that the protozoa-destroying substance should 

 have a specific chemical affinity for the protozoa in question, but little 

 or no chemical affinity for the cells of the host. 



It is impossible to give the details of Ehrlich's seven years of work 

 on this problem; a brief description of the main results must suffice. 

 The first work was done with trypanosomes, the mouse, which could be 

 readily infected, being used as an experimental animal. After testing, 

 with the aid of his assistant, K. Shiga, many hundreds of dye-stufis, 

 some old and some new, one, a member of the benzidin group, was 

 found which retarded the progress of the trypanosome infection for 

 several days. This led to a limitation of the experimentation to a 

 study of the synthetic products of the benzidin group, many of which 

 were made for the first time by Ehrlich and his assistants. The result 

 was the discovery of a substance which exerted an actual curative effect 

 upon trypanosomiasis. This substance, a red dye destroying trypano- 

 somes, was given the name trypan red (trypan roth). If twenty-four 

 hours after mice had been infected with the trypanosome of Mai de 

 Caderas, a single injection of this dye was made, animals which ordi- 

 narily died in four to five days went on to permanent recovery. The 

 blood, twenty-four hours after injection, was found to be free of try- 

 panosomes, which indicated that the effect of the injection was to 

 destroy absolutely every infecting protozoan. Thus was demonstrated 

 for the first time the possibility of completely sterilizing the animal body 

 by a chemical disinfectant without injury to the cells of the host. 



In the course of this work an interesting observation was made. 

 If, instead of a dose necessary to destroy all the trypanosomes, a 

 slightly smaller dose was injected, the trypanosomes would disappear 

 from the circulation for a short time and later reappear. If such 



