NUCLEIC ACIDS IN CHROMOSOMES AND MITOTIC DIVISION 187 



prepared according to Altmann," he showed the affinity of nucleic acid for 

 methyl green and of protein for the acid dye. The relationship between 

 the dye and the cellular substances was also studied^* '^^ in its quali- 

 tative and quantitative aspects/"'^^ The competitive action of protein 

 on the formation of the dye-nucleate salt was shown to be such that a 

 stoichiometric relationship between the amount of dye bound to a cellular 

 structure and its content of nucleic acid could scarcely be expected, par- 

 ticularly since adsorption of dye on the cell surfaces and its solubility in the 

 cellular structures also have to be considered. 



Nevertheless, several papers on the estimation of nucleic acid in the nucleus using 

 quantitative dye measurements have been published. In some cases under strictly 

 standardized conditions a fairly constant relationship has been obtained between 

 the amounts of bound dye in a c\'tological preparation and the nucleic acid content 

 determined according to other methods.^'"** These questions are discussed in detail 

 in Chapter 17. 



While methyl green staining shows a certain specificity as regards the chromosomal 

 DNA, the selective demonstration of PNA with basic dyes is doubtful. Pyronin has 

 been extensively used but cannot be regarded as specific." 



The isolation and purification of specific enzymes attacking the two types of 

 nucleic acid"** has given new opportunities for studying the distribution of DXA and 

 PNA in the chromosomes although the conditions essential in the application of 

 cytochemical methods employing enzymic hydroh'sis must be carefully controlled. 

 Not only must the purity of the enzyme and the absence of proteolytic contaminants 

 be assured, but all other variables capable of modifying the reactions must be ex- 

 amined, e.g., fixation and embedding procedures, pH, time and temperature of diges- 

 tion, etc. 



On the basis of altered stainability effected by enzymic treatment, the 

 presence in chromosomes of both DNA and PNA has been demon- 

 strated.^^-^^ 



" R. Altmann, Arch. Anat. u. Physiol. 13, 524 (1889). 



^* K. Spiro, "tlber physikalische und physiologische Selection." Strassburg, 1897. 



^8 A. Mathews, Am. J. Physiol. 1, 445 (1898); see also M. Heidenhain, Pflugers 

 Arch. ges. Physiol. 90, 115 (1902). 



" L. Michaelis and P. Rona, Biochem. Z. 97, 57 (1919). 



^' J. Loeb, "Proteins and the Theory of Colloidal Behaviour." McGraw Hill, New- 

 York, 1922. 



« E. Hammarsten, G. Hammarsten, and T. Teorell, Acta Med. Scand. 58, 219 (1928). 



" A. Mirsky, Cold Spring Harbor Symposia Quant. Biol. 12, 143 (1947). 



^^ N. Kurnick, J. Gen. Physiol. 33, 243 (1950) ; Exptl. Cell Research 1, 151 (1950). 



^5 N. Kurnick and A. Mirsky, J. Gen. Physiol. 33, 265 (1950). 



■•* L. Michaelis, Cold Spring Harbor Symposia Quant. Biol. 12, 131 (1947). 



" E. Taft, Exptl. Cell Research 2, 312 (1951). 



4«J. H. Northrop, M. Kunitz, and R. M. Herriott, "Crystalline Enzymes," 2nd 

 ed. Columbia Univ. Press, New York, 1948. 



49 J. Brachet, Compt. rend. soc. biol. 133, 88 (1940). 



" J. Schultz, Cold Spring Harbor Symposia Quant. Biol. 9, 55 (1941). 



