NUCLEIC ACID CHEMISTRY CELLULAR LOCALIZATION 



263 



basic dyes {e.g. toluidine blue). 

 Since the sections may con- 

 tain acidic constituents other 

 than nucleic acids, the reac- 

 tion is not specific unless we 

 can find a way of removing 

 only one nucleic acid. This 

 can easily be done by digest- 

 ing away one of the nucleic 

 acids with a specific nuclease 

 (Brachet, 1941a) and com- 

 paring under the microscope 

 sections stained before and 

 after the enzymatic digestion 

 (Fig. 2, b, c). The technique 

 used for the cytochemical 

 detection of RNA with basic 

 dyes (usually Unna's mixture 

 of methyl green and pyronine, 

 which has the advantage of 

 staining DNA green and RNA 

 red) and ribonuclease has 

 been discussed in detail (Bra- 

 chet, 1953). The utilization, 

 in the same way, of deoxy- 

 ribonuclease for the detection 

 of DNA is not so widespread, 

 because of the existence of 

 the much simpler Feulgen 

 reaction. 



Finally, the very high ultra- 

 violet absorption at around 

 2600 A of the purines and 

 pyrimidines has been utilized 

 very elegantly by Caspers- 

 son (1940, 1950) for the 

 detection of nucleic acids: the 

 principle, of course, is to take 



Fig. 2. Sections of intestinal mu- 

 cosa (mouse) ; a: Feulgen reaction; 

 b: Stained with methyl green- 

 pyronine; c : same as b, but treated 

 with ribonuclease before staining : 

 cytoplasmic basophilia has disap- 

 peared. 



Literature p. zgg 



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