ON SPECIFIC THERAPEUTICS. 85 



into acetic acid and aniline, and it cannot, 

 therefore, be nearly as effective as it is in the 

 mouse. Nevertheless, the results obtained in 

 the mouse are so excellent that they must 

 encourage us to energetically pursue the path 

 of these discoveries. 



I mentioned in my last lecture that it is pos- 

 sible to obtain strains of trypanosomes which 

 are resistant to these active substances. Studies, 

 which I have carried out with Dr. Rohl and 

 Dr. Browning, have shown this resistance to be 

 of a very high degree. Thus, atoxyl-fast strains 

 show no sign of being influenced by the highest 

 doses of atoxyl which are applicable to mice. 

 I gave you the explanation for this resistance, 

 viz., that it is the result of a decrease in the 

 avidity of the trypanosomes for these trypano- 

 cidal substances. Further, I pointed out that, 

 apart from this resistance, the parasites' pro- 

 toplasm, although not their nuclei, had become 

 hyper-sensitive towards the arsenical prepara- 

 tion. Thus we meet with an important instance 

 of association, in one and the same cell, of 

 resistance and hyper-sensitivity. This associa- 

 tion, which is of late years proving to be of 

 increasing importance in the question of 

 mammalian immunity, is therefore present 



