50 EXPERIMENTAL RESEARCHES 



lecithin is not at the disposal of the cobra ambo- 

 ceptor. 



I will now discuss a further similar case, 

 namely, that of certain phenomena observed by 

 me in the course of my studies on trypanosomes. 

 As some of you may know, I have, together 

 with my assistants, Dr. Rohl and Dr. Browning, 

 proved that trypanosomes can be rendered 

 resistant towards all those agents which are 

 employed for curative purposes. If, e.g., a 

 mouse infected with trypanosomes is treated 

 with fuchsin, the parasites disappear, but 

 return after a longer or shorter interval. If 

 the treatment is then repeated, a similar result 

 is observed. Thus this alternation of relapse 

 and treatment can be repeated several times, 

 though not indefinitely, for in course of time the 

 effect of the fuchsin becomes more and more 

 unsatisfactory and finally disappears altogether. 

 If now the trypanosomes are transferred from 

 such an animal to normal mice, these parasites 

 are now, even in the normal mouse, found to be 

 no longer capable of being influenced by fuchsin. 

 There has thus been formed a fuchsin-resistant 

 or " fuchsin-fast " strain. I have chosen this 

 expression because I found that such a resis- 

 tance, once acquired, appears to remain un- 



