CYTOCHEMICAL TECHNIQUES FOR NUCLEIC ACIDS 63 



same nucleic acid molecule, and less between those from adjacent nucleic 

 acid molecules. 



7. Quantitative Aspects 



From the variables discussed above, we may conclude that dye binding 

 in tissue sections, at least under the conditions generally used, cannot be 

 trusted to give an accurate picture of the amount of nucleic acid present. 

 In many cases, however, a rough indication of nucleic acid concentration 

 may be all that is desired. In such cases basic dye binding will continue to 

 be extremely useful, as it has been in the past. It is obvious from basic 

 staining that more cytoplasmic PXA occurs in rat pancreas than liver, for 

 example, or in root meristems than in differentiated regions. Also where 

 protein-nucleic acid ratios are not markedly altered or the type of protein 

 changed, estimates of the PNA concentration, made from photometric de- 

 terminations of dye bound, may be reasonably accurate. A good corres- 

 pondence between ultraviolet absorption and azure B binding was found 

 in cytoplasm of mouse oocytes in various stages of growth^* but a very 

 poor correlation in cytoplasm of human liver." Yolk platelets, at least in 

 some cases, are only weakly basophilic, yet chemical determinations have 

 shown them to be rich in PNA.** 



In measurements on nuclei, basic dyes may show poor correlation with 

 data obtained by ultraviolet absorption or the Feulgen reaction. As dis- 

 cussed later, the Feulgen reaction demonstrates a rather surprisingly regu- 

 lar stoichiometry with DNA. Basic dye binding, after ribonuclease, may 

 be compared with the Feulgen reaction, run on adjacent sections. Methyl 

 green, and azure B gave values for small, dense erythroblast nuclei in new- 

 born mouse liver about 50% higher than found for nuclei of liver paren- 

 chyma. The Feulgen reaction, however, gave no significant difference 

 between the two types of nuclei. Similarly, about 35% more methyl green 

 was bound to metaphase chromosomes from the small intestine than ex- 

 pected from Feulgen measurements. A better correlation between methyl 

 green, Feulgen, and ultraviolet measurements was found by Frazer and 

 Davidson*^ for rat liver and kidney, but widely different nucleic acid 

 concentrations were probably not encountered. Preliminary photometric 

 measurements with gallocyanine-chrome alum have shown a better cor- 

 respondence to Feulgen staining than with other basic dyes;®" its use for 



5« M. Flax, Ph.D. Thesis, Columbia University, New York, 1953. 



" A. W. Pollister, J. Post, J. G. Benton, and R. Breakstone, J. Natl. Cancer Inst. 



12, 242 (1951). 

 " J. Panijel, "Le nti^tabolisme de nucl^oprot^ines dans la gam^togendse et la fdcon- 



dation." Hermann, Paris, 1951. 

 "S. C. Frazer and J. N. Davidson, Exptl. Cell Research 4, 316 (1953). 

 «o H. Swift, Intern. Rev. Cytol. 2, 1 (1953). 



