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Mesnil and Nicolle, in their excellent work on the action of 
Benzidines' (Diazo-colouring matters), have already pointed out that 
even the slightest difference in the constitution of a substance may 
have a great effect upon its trypanocidal action. This point is 
particularly well illustrated in the two following compounds, of which 
III has a very distinct effect upon the trypanosomes, while IV is 
practically non-trypanocidal. 
Ill 
Our work upon the aniline colouring matters was undertaken 
with the intention of starting with an indifferent organic compound, 
that is, one which has no effect upon the trypanosomes, and of 
combining with it various radicles in the hope of finding one which 
would have definite trypanocidal properties. 
Our work has led us to the conclusion that the NH^ group is sue 
an active trypanocidal radicle, and we are accustomed to call it the 
‘ trypanophobe ’ group. 
For our starting point we took ‘ Phenolphthaleine, V, whici on 
being injected into the alkaline tissues, changes into, VI, a Tripheny 
methane. This compound is of the same character as Malaclnte 
Green and contains no NFI2 groups ; we found it to be without e ect 
upon the trypanosomes. We then proceeded to Fluorescein, 
and to different halogenic fluorescein derivatives, such as Fosm, 
Floxin, Sic.; here, too, there was no trypanocidal effect. 
'Rhodamine,’ VIII, was used, it was found to have a very is me 
effect upon the parasites ; it possesses NH^ groups. 
