412 COLLECTED STUDIES IN IMMUNITY 



" chromophore " group. Concerning the deatils of the various types 

 of chromophores I refer the reader to the admirable work of Nietzki. 

 I may, however, say here that, as a rule, the action of the chromophore 

 groups as such does not become manifest if the group is part of a 

 molecule very poor in carbon atoms. Hence colored combinations 

 are rare in the fatty series; they belong almost exclusively to the 

 aromatic series (Nietzki). The presence of a chromophore group 

 does not, however, by itself suffice to produce true dyes. Thus 

 azobenzol, which possesses the chromophore azo group, N=N, is 

 no dye, because it possesses no affinity for tissues. For this reason 

 Nietzki terms azobenzol a "chromogen," i.e., a combination which 

 becomes a true dye when suitable groups are introduced. Radicals 

 which have the power to develop the nature of a dye are called 

 " auxochrome " radicals (Witt). Thus far we know but two, namely, 

 the OH group which produces dyes of an acid character, and the 

 amido group which produces basic dyes. In contrast to this it is 

 found that other salt-forming groups are not auxochromic. This 

 holds true not only tor acid complexes, such as the carboxyl group 

 and the radical of sulpho acids, but also for certain basic radicals 

 as NH 4 , CH 2 -NH 2 , CH 2 -N-(CH 3 ) 2 , and 0-CH 2 N (CH 3 ) 2 . 



From every chromogen, therefore, two series of dyes may be de- 

 rived, acid and basic, each acid derivative having an analogous basic 

 one. Thus 



Acid Basic 



Oxyazobenzol Amidoazohenzol 



Dioxyazobenzol (resorcin yellow) Diamidoazobenzol (chrysoidim 



Rosolic acid. Rosanilin 



Thionol Thionolm 



Aposaffranon Aposaffranin 



If several similar auxochromes are introduced into a chromogen 

 it will be found that up to a certain point the intensity of the shade 

 and the affinity for the tissues increases with the number of groups in- 

 troduced; thus, amidoazobenzol yellow; diamidoazobenzol orange;, 

 triamidoazobenzol brown . 



Witt's observations extended only to the question whether and 

 under what conditions a body is colored. Nietzki went a step fur- 

 ther and showed that the simplest azo bodies, as also all the most 

 simply constituted dyes, possess a yellow color. He showed that 

 the tint deepens not only with the increase in auxochrome groups 

 just mentioned, but also with the accumulation of carbon atoms in 



