INHERITANCE IN TRYPANOSOMES 695 



Large quantities of lice were transferred from rats infected 

 with this drug-resistant race to normal rats. The latter became 

 infected in a certain number of cases and the result differed 

 according to the mode of infection. In two cases the trans- 

 mission was merely mechanical, i.e. the trypanosomes were 

 carried on the mouth parts of the lice and directly inoculated 

 into the new host. In both these cases the drug-resisting power 

 was maintained. On the other hand, in the majority of cases the 

 transmission was indirect, i.e. the trypanosomes passed through 

 a developmental cycle in the intermediate host before the latter 

 became infective. After this cycle had been passed through, 

 it was found that the acquired character of resisting the drug 

 was completely lost. Accordingly when rats were infected by 

 these lice, the trypanosomes which developed in their blood 

 were quite normal and an injection of arsenophenylglycin 

 caused their disappearance from the circulation ; the resistant 

 race of trypanosomes kept as a control was quite unaffected 

 by a similar injection. 



In addition to these transmission experiments, Gonder 

 attempted to ascertain at what period in the louse the trypano- 

 somes lost their power of resisting the drug. For this purpose 

 several hundred lice were taken from a rat infected with the 

 resistant race. Each day about 50 to 100 of the lice were 

 triturated in normal saline solution and the emulsion injected 

 into healthy rats. The animals became infected with the try- 

 panosomes after varying periods of incubation. They were then 

 injected with arsenophenylglycin in order to ascertain whether or 

 not the drug-resisting power had been maintained. The drug- 

 resisting power was maintained during the first ten days after 

 the lice had been taken from the rat ; consequently, all the 

 rats which received injections during this period became 

 infected with the drug-resisting race of trypanosomes. Eleven 

 and twelve days after the lice had been removed the drug- 

 resisting power was noticeable in some of the infected rats but 

 not in others, whereas all rats into which lice were injected 

 that had been removed more than twelve days from the original 

 animal became infected with a perfectly normal race of the 

 rat-trypanosome. The poiver of resisting the drug had disappeared 

 completely and as a result when each of these rats was injected 

 with arsenophenylglycin the trypanosomes disappeared from 

 its circulation. 



