90 EXPERIMENTAL RESEARCHES 



strain is also resistant to a number of sub- 

 stances related to atoxyl, but otherwise showing 

 widely different chemical characteristics. Evi- 

 dently, therefore, the arsenic acid radical here 

 represents the point of attack which is common 

 to this series of substances. It is the arsenical 

 radical as such, which is bound by the chemo- 

 receptors. These chemo-receptors, must, how- 

 ever, be regarded as of a simpler structure than 

 the toxin-receptors. They do not show a similar 

 degree of independence ; they cannot therefore 

 become increased in chronic intoxications, and 

 since they are sessile, they cannot be thrown off 

 into the blood. The number of such chemo- 

 receptors for poisons which a trypanosome cell 

 possesses, represents the number of points of 

 attack. By means of the resistant strains we 

 can count off one by one these groups that are 

 open to attack. 



The discovery of any trypanocidal substance 

 will always be the result of chance and experi- 

 ment. Every point of attack may, of course, be 

 liable to be attacked by a host of different bodies, 

 all of which have one specific group in common. 

 It must be the goal of our experiments to 

 search, by systematic chemical researches, for 

 the most suitable substances, and thus to dis- 



