ON SPECIFIC THERAPEUTICS. 51 



altered even after as many as a hundred succes- 

 sive passages. We have up to now produced 

 similar strains resistant to arsenical preparations, 

 to trypan-red and trypan-blue as well as to 

 fuchsin. In my next lecture I shall enter more 

 fully into the importance of these strains. 



I will here discuss one point only which is 

 connected with to-day's subject, viz., the 

 question as to the origin of the resistant strains. 

 I have made the interesting observation on an 

 arsenic-fast strain which was obtained by several 

 years' treatment with atoxyl, and which was 

 then made still more resistant by means of a 

 very active arsenical preparation (No. 379), 

 which I shall briefly call " Trypocid." This 

 strain is distinguished from normal trypanosomes 

 in that it is no longer influenced by this highly 

 active arsenical preparation. One would have 

 expected that also in test-tube experiments, it 

 would have shown a high resistance towards 

 trypocid. Of course, such an examination could 

 only be carried out by comparing it with other 

 strains of trypanosomes. For obvious reasons 

 I employed the original strain from which this 

 resistant one had been derived, and which had 

 been cultivated in the laboratory. I chose two 

 animals containing about the same number of 



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