Maech 27, 1914] 



SCIENCE 



445 



there is no evidence of the ill effect of the 

 dye. 



If now instead of trypan blue we employ 

 the brilliant blue dye azo-blue whose con- 

 stitution is 



OH OH 



CHs CHs III 



NaOaS 



we are met by a striking difference. 

 Neither within minutes or hours after the 

 intraperitoneal injection of such a dye is 

 any trace of color to be seen from the dye, 

 and the repeated injection of the dye over 

 a long period of time do€S not in any way 

 change this negative result. The autopsy 

 of such an animal shows indeed that we 

 have heaped upon it a large quantity of a 

 colored foreign body, for the dye has re- 

 mained on the whole where it was injected, 

 that is, in the peritoneum and the structures 

 connected with it. Why this difference? 

 Several notions have been advanced in 

 explanation of the action of vital stains. 

 Primarily we have to do with the ideas, 

 first, that a chemical union exists between 

 the dye molecules and some portion of the 

 cell protoplasm, and, second, the theory 

 that dyes owe their ability to stain vitally 

 to some physical property by virtue of 

 which they can penetrate the cell. The 

 name of Ehrlich is connected with the first 

 of these two views, while that of Overton 

 is identified with the second, and we may 

 mention here that the commonest physical 

 rather than chemical explanation of vital 

 staining has been that the dyes in question 

 are soluble in fat or fat-like bodies, a layer 

 of which was assumed to envelop the cell. 

 While this explanation may have been con- 

 vincing in the explanation of vital staining 

 obtained by the earliest known vital stains 

 (methylene blue and neutral red) we are 



aware now that both of the assumptions in- 

 volved in it were gratuitous, for neither are 

 the benzidine dyes soluble in fats or lipoids 

 nor are the majority of the cells of the body 

 surrounded by a layer of these substances. 

 If, then, in spite of the above, we must 

 maintain that after all physical factors play 

 a predominant role in the vital staining 

 produced by the azo or benzidine dyes, it is 

 for reasons quite apart from those involved 

 in Overton's lipoid theory. 



The chemical explanation of a vital stain 

 presupposes that there exists between some 

 element of the protoplasm of the cell, the 

 ehemo-receptor in the sense of Ehrlich, and 

 some part of the dye molecule a combina- 

 tion, such as we are accustomed to see take 

 place between two bodies in accordance 

 with the laws of formal valence. It is only 

 necessary to show how important such an 

 explanation is in the mind of Ehrlich by 

 mentioning the fact that he assigns the 

 therapeutic effects of the drug salvarsan 

 primarily to an affinity which he assumes 

 to exist between the parasites of syphilis 

 and a precise part of the salvarsan mole- 

 cule; namely, the ortho-amido-phenol con- 

 figuration. The application of this prin- 

 ciple in an explanation of the vital stain 

 produced by trypan blue must lead us to 

 maintain that a similar configuration, i. e., 

 the peri-amido-naphtol configuration, is 

 really responsible for the union between 

 dye and cell which gives us the vital stain 

 here. We can dispense with such reason- 

 ing shortly. 



Evidence which would appear to con- 

 cern the efficacy of a peri-amido-naphtol 

 ceptor is furnished by the brilliant vital 

 staining produced by the dyes Nos. 1824, 

 1835 and 1846, in all of which the hydroxyl 

 and amido groups are in a peri position to 

 one another, and the azo bond at position 

 II. 



