ON SPECIFIC THERAPEUTICS. 91 



cover the " optimum centres." This problem is 

 by no means an easy one, since according to 

 my experience of many years, which agrees 

 entirely with that of Mesnil, different animal 

 species have different optima, and therefore the 

 work must be specially done for each species of 

 animals and each kind of trypanosomes. Thus, 

 e.g., in the mouse, Trypanosoma gambiense is far 

 more easily attacked by arsenical preparations 

 than the other strains of animal-pathogenic 

 trypanosomes, whilst fuchsin and its relatives 

 show an exactly opposite behaviour. Still, in 

 spite of all these difficulties, the problem is not 

 insoluble, since there are only a limited num- 

 ber of animal species and of trypanosomes ; we 

 may, therefore, confidently cherish the hope 

 that the united forces of the observers who are 

 at work on this subject in various laboratories 

 will ultimately succeed in attaining the victory 

 over sleeping-sickness, which is practically the 

 most important. 



Especially with a view to practical thera- 

 peutics the knowledge of the different points 

 of attack is necessary, since it furnishes us 

 with the possibility of fighting the disease by 

 the combination of several chemo-therapeutic 

 agents. 



