150 Biological Stains 



Basic fuchsin is also employed as a chemical reagent in a deter- 

 mination which is coming to be of considerable interest to the 

 biologist. Basic fuchsin is the main constituent of Schiff's re- 

 agent, often employed for the detection of aldehydes, although not 

 an absolutely specific reagent for the purpose. In preparing this re- 

 agent, basic fuchsin is reduced through the action of sulfite to a 

 colorless form, having the type of the formula for leuco-fuchsin 

 which is given at the middle of page 31, (The formula there given 

 for leuco-fuchsin, however, is not exactly that of Schiff's reagent, as 

 it is believed that the sulfite radical in some way enters into its com- 

 position.) In the presence of aldehyde some chemical reaction not 

 wholly understood takes place which evidently restores the quino- 

 noid structure of the molecule and, accordingly, the color of the 

 compound. Apparently a slightly different dye from the basic 

 fuchsin is thus produced, since the color is violet rather than pure 

 red. 



This reaction is of interest to the bacteriologist, as basic fuchsin 

 is employed similarly in the Endo medium for distinguishing be- 

 tween members of the colon-typhoid group of bacteria. This 

 medium contains lactose, which is not acted upon by the typhoid 

 organism but is fermented by organisms like Bacterium call. It 

 has been known for many years that these lactose fermenting 

 organisms of the group restore the red color of the medium, while 

 the non-lactose-fermenters do not. The suggestion was naturally 

 made that this Endo reaction might depend upon the production 

 of aldehyde by the organisms, but for years no one was able to 

 demonstrate the presence of aldehyde in such cultures. Neuberg 

 and Nord (1919) suggested, however, that aldehyde might be 

 produced but not ordinarily accumulate in sufficient quantity to 

 be detected; and that the sulfite in the medium might act as a 

 ''trapping agent'* so as to allow it to accumulate. This has since 

 been verified by Margolena and Hansen (1933). Apparently, 

 therefore, the Endo medium is a biological application of Schiff's 

 reagent. 



Feulgen and his associates (Feulgen and Rossenbeck, 1924; 

 Feulgen and Voit, 1924) employed this compound of basic fuchsin 

 and sulfurous acid in histological technic, regarding it as a micro- 

 chemical reagent for detecting the presence of aldehyde-like sub- 

 stances in the nuclei. Feulgen called this the "nucleal reaction," 

 the ending "-al" indicating the aldehyde-like nature of the sub- 

 stance which he considered the reaction to demonstrate. This 

 interpretation of the Feulgen reaction is now regarded as only 

 part of the story; the significance of the desoxyribosenucleic acid 

 demonstrated by the method is appreciated more today than it 

 was when Feulgen proposed the method. 



As a matter of fact, the Schiff reagent, employed by some modi- 

 fication of the Feulgen technic, has given histochemistry its 



