GENUS: TRYPANOSOMA 461 



hand, the pentavalent arsenic and antimony compounds are much less 

 toxic, do not cause the trypanosomes to disappear at once, and have no 

 trypanocidal action. This indicates that if the arsenic or antimony 

 compounds are in the form of R.As = 0, symptoms of toxicity appear 

 at once and trypanosomes disappear rapidly. If they are in the form of 



/OH 

 R.As = a much longer time is required. It is concluded that during 



\0H 

 the interval or latent period the pentavalent compounds are being reduced 

 in the body to trivalent ones. In the case of the arsenobenzol derivatives 

 (salvarsan, etc.), which act slowly and have no trypanocidal action in 

 vitro, it is believed that an oxidation to the trivalent forms takes place 

 {R.As=:As.R becomes R.As:=0). In the case of atoxyl, which again 

 shows a latent period before it acts, and which has no trypanocidal action 

 in vitro, the process seems to be one of reduction to the trivalent form. 

 Terry (1915) showed that if atoxyl and blood were incubated together, the 

 mixture acquired marked trypanocidal properties. 



In animals such as rats and mice the various salvarsan and neo- 

 salvarsan compounds vary in their toxicity and in their therapeutic 

 efficiency. The toxic doJ^e for these animals varies from about 0-2 to 

 0-6 gram per kilogram of body weight, while a dose which is approx- 

 imately one-tenth of this will clear the blood of pathogenic trypano- 

 somes in about twenty-four hours. The toxic dose of tartar emetic is 

 about 0-04: gram per kilogram of body weight, and a dose of 0-02 gram 

 per kilogram will clear the blood of trypanosomes in about fifteen to thirty 

 minutes. 



A drug (Bayer 205), which was first introduced in Germany by 

 Haendel and Joetten (1920), and Mayer and Zeiss (1920), appears to 

 have an action on trypanosomes which is more specific than that of any 

 drug hitherto employed. It is claimed that cures can be uniformly brought 

 about in small animals, and also in horses suffering from dourine. Further- 

 more, in small animals the single dose (0-003 gram per kilogram of body 

 weight) necessary to bring about a cure is only one-sixtieth of that which 

 can with safety be given to the animals. The ratio between the minimal 

 therapeutic dose and the maximum tolerated dose is thus 1 : 60. In 

 this respect, again, the drug is superior to any trypanocide which has 

 been used before. The writer (19216) tried the drug in the case of mice 

 infected with a very virulent strain of T. equvperdum, and was able to 

 confirm the statement of the German investigators. 



Kleine and Fischer (1922) and Kleine (1924) find that the drug is 

 efficacious in the case of human trypanosomiasis, and also gives promising 

 therapeutic and prophylactic results in the disease of domestic animals. 



