THE NUCLEIC ACID CONTENT OF TISSUES AND CELLS 45 



for 60 hours after fertilization, while the DNA content doubled every 

 hour in the first 10 hours, and at 10 and 40 hours indicated that there were 

 900 and 3550 cells per embryo, respectively. Using an isotopic dilution 

 method to measure DNA and a chromatographic method for PNA, Mar- 

 shak and Marshak^^^ find that Arhacia eggs contain 24.4 X 10~^ Mg- PNA 

 per egg and 8.1 X 10~^ jug. DNA per egg. In human adrenal tissue, the 

 PNA-P and DNA-P concentrations are 20.5 to 41.3 and 12.2 to 18.5 mg./ 

 100 g. tissue, respectively.225 The PNA and DNA fractions in Mycobacte- 

 rium tuberculosis are reported to contain 29.8% and 6.0% of the total 

 phosphate content of the organisms.^^^ Vendrely and Tulasne^^'' find that 

 the dwarf, or L-forms of Proteus (P 18) have an average PNA/DNA ratio 

 of 0.14 as compared with the ratio of 2.50 in the normal forms. 



A warning of the danger of applying the Schmidt and Thannhauser 

 method to all tissues without preliminary investigation has been given by 

 Drasher.^-^ Her results with mammary tumor tissue from C3H mice led 

 her to conclude that a significant amount of the DNA was being hydro- 

 lyzed by the alkaline digestion and was passing into the PNA fraction, 

 thus producing a much higher PNA-P/DNA-P ratio for the Schmidt and 

 Thannhauser than for the Schneider method (see also footnote c, Table II) . 



The DNA content of tissues is being used increasingly as a means of 

 determining changes in cell number in growing tissues. In the virgin mouse 

 uterus, Drasher229 found that the total DNA content or cell number in- 

 creased most rapidly between 2}^^ and 6 months, and that the PNA/DNA 

 ratio was higher in the stimulated stages (proestrus, estrus, and early 

 metestrus) than in the unstimulated stages (late metestrus and diestrus). 

 Nowinski and Yushok^^'' measured the DNA content per nucleus in wings 

 and legs of 5- to 12-day-old chick embryos by the Schneider method and 

 obtained considerably higher average values than those previously re- 

 ported^^^"-^' for chick embryonic cells. The time required to enable the 

 DNA content to double in amount varied from 25 hours for legs in the 

 6- to 7-day embryos to 31 hours for both legs and wings in the 11 -day 

 embryos.''" 



2" A. Marshak and C. Marshak, Exptl. Cell Research 5, 288 (1953). 



"6 J. N. Davidson, unpublished results. 



"6 F. Winder and J. M. Denneny, Nature 174, 353 (1954). 



2" R. Vendrely and R. Tulasne, Nature 171, 262 (1953). 



"8 M. L. Brasher, Science 118, 181 (1953). 



"9 M. L. Brasher, Proc. Soc. Exptl. Biol. Med. 84, 596 (1953). 



230 w. W. Nowinski and W. B. Yushok, Biochim. et Biophys. Acta 11, 497 (1953). 



"" J. N. Bavidson, I. Leslie, R. M. S. Smellie, and R. Y. Thomson, Biochem. J. 46, 



xl (1950). 

 232 A. E. Mirsky and H. Ris, Nature 163, 666 (1949). 

 2" W. E. J. Phillips, W. A. Maw, and R. H. Common, Can. J. Zool. 31, 167 (1953). 



