VARIOUS ARSENIC COMPOUNDS 243 



phenomenon, the trypanosomes possess in addition a chemoceptor with an 

 affinity toward acetic acid, and therefore any strain which has become 

 resistant toward arsenophenylglycin has become not only arsenic fast but 

 has become immune to all combinations which like arsenophenylglycin 

 contain an acetic acid radicle. 



The action of an arsenical compound depends upon its being anchored 

 not only by means of one of its groups but by many groups, "Just as a 

 butterfly that is to be mounted must be fixed by more than one attach- 

 ment. First a needle must be passed through its body and then successive 

 fixation through the animal's wings is necessary." In this sense Ehrlich 

 speaks of primary and secondary haptophores. In arsenophenylglycin 

 the primary anchoring group is the receptor of the acetic acid radical 

 which delivers the arsenic element to the cell. Whereas for the try- 

 panosomes it is this acid group which plays the main role, for the spiro- 

 chete, it is the hydroxyl group, placed in the para-position of the trivalent 

 arsenic molecule (arsenophenol). 



As = As 



\/ \/ 



OH OH 



Arsenophenol. 



By the introduction of different elements or combinations into the 

 above formula (as iodin or an amido group) the toxic action of the com- 

 pound can be further diminished, whereas the spirillocidal property is 

 greatly enhanced. In this manner, Ehrlich and Bertheim developed the 

 preparation 606 (salvarsan) which is the dihydrochloride of dioxy- 

 diamidoarsenobenzol. 



As = As 



NH 



NH, 



OH OH 



As = As 



C1HNH ; 



NH 2 C1H 



OH OH 



Dioxydiamidoarsenobenzol. Dioxydiamido-arseno-benzene dihydrochlor- 



ide (Salvarsan). 



Dioxydiamidoarsenobenzol is a canary yellow powder undergoing oxidation very 

 readily so that it is kept in small vacuum tubes. It is insoluble in water but soluble 

 if sodium hydroxide is added. The hydrochloric acid salt, salvarsan, is soluble in 

 water giving a clear yellowish solution. It is acid in reaction and absorbed by the 

 system with difficulty (Hata). On the addition of sodium hydrate first a monochloride 

 and then a neutral salt in the form of a flocculent precipitate results. More of the hy- 

 droxide redissolves, the precipitate giving a clear solution of the alkali salt; its reaction 

 is strongly alkaline. It makes no difference whether the dioxydiamidoarsenobenzol 

 is dissolved in sodium hydrate or whether the hydrochloric acid salt is made alkaline 



