ON SPECIFIC THERAPEUTICS. 55 



trypanosomes. If, however, this counterbalancing 

 effect of the mouse's organism is removed, the 

 poisonous agent can with full force seize the 

 trypanosomes. I would even go so far as to say 

 that we have to do in this case with a biological 

 adjustment of the greatest delicacy, and that 

 Nature limits herself to the most strictly neces- 

 sary gradations and never allows a reduction of 

 the affinity to its minimum. 



As a proof of this I may mention a similar 

 biological observation. I sent my resistant 

 strain to the Liverpool School of Tropical 

 Medicine, where it was found that the atoxyl- 

 resistant strain showed the resistance as 

 described by me only in mice but not in rats. 

 This result was, of course, very surprising, but 

 you will easily understand it on the basis of the 

 previous results, by the supposition that the 

 avidity of the rat's organism for trypocid is 

 inferior to that of the mouse. In the rat, 

 therefore, the trypanocidal effect is preponderant, 

 since the trypanosomes are still able to seize 

 upon the poison. 



Let me now pass on to a very different field 

 of research. I should be guilty of carrying 

 owls to Athens, if I were here to speak in detail 

 of the nature and importance of Jenner's great 



