Organic Substances 81 



is a pseudo-reaction, not resistant to acid and alcohol. Also, 

 the recolorization of Schiff's reagent by purines could not be 

 confirmed.^^ That the active dye is really an aldehyde ad- 

 dition product can be proved by blocking the reaction with 

 specific carbonyl reagents. ^^^ Cyanide is especially eflFec- 

 tive.^^^ The successful substitution of Schiff's reagent by 

 other reagents has been mentioned. The aldehyde compound 

 must come from DNA; if the latter is removed by specific 

 enzymes, the Feulgen reaction is abolished. 



3. The dye prepared in the test tube from hydrolyzed 

 DNA and Schiff's reagent is soluble (although not dialyz- 

 able).^^^ However, this does not apply to tissue sections in 

 which nucleic acid is present in firm chemical union with 

 proteins and in a completely insoluble state. It is not made 

 soluble by mild acid hydrolysis. ^^^ The nonnal HCl from a 

 Coplin jar in which nine slides, carrying several large tissue 

 sections each, were hydrolyzed for 12 minutes did not show 

 the slightest trace of color with Schiff's reagent. There is no 

 reason to assume that a degraded but insoluble DNA would 

 form a soluble addition compound with Schiff's reagent; in 

 fact, there is evidence to the contrary. ^^^ In Coujard slides, 

 marks made with DNA of high purity and fixed in formalin- 

 alcohol gave an intense and sharp reaction, with absolutely 

 no indication of diffusion; marks made with RNA and several 

 proteins were completely negative. Of course, it is conceiv- 

 able that traces of moderately soluble fragments may be lib- 

 erated during hydrolysis and converted into dye which may 

 stain structures in the immediate proximity. However, it is 

 difficult to explain why the infinitesimal concentration of dye 



99. Barber, H. N., and Price, J. R.: Nature, 146:335, 1940. 



100. Lessler, M. A., and Kopac, M. J.: Anat. Rec, 108:531, 1950; Less- 

 ler, M. A., and Kopac, M. J.: ibid., 108:578, 1950; Lhotka, J. F., and 

 Davenport, H. A.: Stain Technol., 26:35, 1951. 



101. Gomori, G.: Unpublished. 



102. Ely, J. O., and Ross, M. H.: Anat. Rec, 104:103, 1949. 



103. Brachet, J.: Experientia, 2:142, 1946. 



104. Li, C., and Stacey, M.: Nature, 163:538, 1949. 



