253 
6. SODIUM-p-HYDROXYL-PHENYL-ARSENATE* AND SERUM 
>Na 
Sodium-p-hydroxyl*phenyl- 
arsenate = 
OH 
Skrcu Used. 
Aksenic Estimation 
IN Precipitate. 
Donkey serum 
Donkey serum 
Donkey serum 
Donkey serum 
Donkey serum 
Donkey serum 
Donkey serum 
arsenic absent 
arsenic absent 
arsenic absent 
arsenic absent 
arsenic absent 
arsenic absent 
arsenic absent 
It is evident from the foregoing experiments that a combination 
takes place respectively between proteins and Atoxyl, mono 
acetylated Atoxyl, and mono-benzoylated Atoxyl; whilst no 
combination occurs respectively between these proteins and sodium 
arsenate, acetyl-benzoyl Atoxyl. and sodium-p-hydroxy-plienyl- 
arsenate. 
It might be mentioned that there is a considerable difference in 
the results obtained by the treatment of Trypanosomiasis by means 
of the above-mentioned compounds. Whereas Atoxyl and mono 
acetylated Atoxyl act promptly on the parasites, the effect of sodium 
arsenate is less pronounced, that of sodium-p-hydroxy-phenyl-arsenate 
is nil. 
The analogy between the way in which these compounds beha 
with proteins, and their action on trypanosomes, is very suggestive. 
We are, hence, led to believe that this combination with the proteins 
is of importance in trypanocidal drugs, and have now to consider 
Atoxyl and its derivatives become attached to the proteins. 
Ehrlich** has compared the action of a drug to that of a dye. 
know that it is necessary for a dye to possess a chromophoric group-- 
a chemical radical which causes it to be coloured—and a chromogemc 
* Our ihanks arc due to Messrs. Burroughs, Wellcome & Co., who kindly supp! 
lois drug. 
