CYTOCHEMICAL TECHNIQUES FOR NUCLEIC ACIDS 65 



information, but in other cases they may not. For this reason results ob- 

 tained from measurements of dye intensity should be interpreted with 

 caution, and wherever possible checked by independent methods. 



III. The Feulgen Reaction 



In spite of the tremendous number of studies on the Feulgen reaction, 

 many points concerning it are still obscure. A few years after the published 

 description by Feulgen and Rossenbeck^* in 1924, it was employed by a 

 great many cytologists for chromosome studies, where the interference of 

 cytoplasmic staining could be eliminated, and chromosomal material could 

 be distinguished from nucleoli. In the last few years the Feulgen raection 

 has also been widely used, in conjunction with microphotometric instru- 

 ments, to estimate the amounts of DNA in nuclei. To evaluate such studies, 

 variables affecting Feulgen intensity should be examined in some detail. 

 For a recent review, see Lessler.*® 



1. Chemistry 



The mechanism of the Schiff reaction with aldehydes, which forms the 

 basis for the Feulgen reaction, was studied by Wieland and Scheuing.^'' 

 According to the theory proposed, the Schiff reagent, formed by the reac- 

 tion of SO 2 with an acidic solution of basic fuchsin, produces a colorless 

 compound, the N-sulfinic acid of p-fuchsinleucosulfonic acid, with the for- 

 mula shown below: 



NH 



H,N</ ^— C— <C >NH2 — - 



NH. 



A 



SO3H 



«6 R. Feulgen and H. Rossenbeck, Z. physiol. Chem. 135, 203 (1924). 



««M. A. Lessler, Intern. Rev. Cytol. 2, (1953). 



" H. Wieland and G. Scheuing, Ber. B54, 2527 (1921). 



