692 COLLECTED STUDIES IN IMMUNITY. 



made up of a large number of individual functions, which, in the 

 form of different chemo-receptors are scattered amongst the nutri- 

 receptors. I believe that these two main groups cannot but be 

 closely related, and for the following reason. 



Trypanosomes of different origin, as they are cultivated in 

 different laboratories, usually from the outset behave differently 

 toward a particular therapeutic substance. The first strain of 

 trypanosome with which I worked, Mai de Caderas, had no resistance 

 whatever against trypaii red, and this substance could be employed 

 to effect a cure. This still holds true. Similar favorable results 

 were obtained by Jakimoff in Russia, while Uhlenhuth obtained 

 absolutely no result with this substance on the strains which he used. 

 We are therefore dealing with natural differences in the various 

 strains. Despite the fact that my strain has now been passed through 

 normal mice for many years, it can still be cured by trypan red just 

 as well as ever. This shows that the difference is not entirely 

 artificial. On the other hand, my Nagana strain could formerly 

 not be healed by trypan red, and cannot be healed by that substance 

 ROW. However, on transforming this Nagana strain into a relapse 

 strain, we were surprised 'to find that this property, which had per- 

 sisted for many years, become altered within 14 days. This proves 

 that the chemo-receptors really are related to the constitution of 

 the protoplasm, and undergo alterations when we alter the con- 

 stitution of the protoplasm. 



Whether the reverse holds true, that is, whether, by influencing 

 the chemo-receptors we can alter the cell substance, particularly the 

 nutri-receptors, has not yet been definitely decided. Browning, to 

 be sure, has observed that by means of serum reactions one can 

 differentiate the fuchsin strain from the atoxyl strain, and both from 

 the original strain. Careful investigation subsequently showed, 

 however, that the changes in question were not specific alterations 

 related to the fuchsin or to the arsenic, but alterations which cor- 

 respond to the relapse mutation described above. These are due to 

 the fact that during the treatment it often happens that the mice 

 suffer relapses, which in turn lead to the formation of relapse strains. 



This brings me to the close of my paper. I am well aware that 

 what I have offered you has been quite fragmentary, but this could 

 hardly be otherwise, for the adequate discussion of this theme would 

 mean the recapitulation of an almost endless amount of work. My 

 object in presenting this subject has been to show you that we are 



