THE NUCLEIC ACID CONTENT OF TISSUES AND CELLS 27 



Bi2 and vitamin C, is the considerable reduction in the PNA/DNA ratio 

 characteristic for the tissue (Table VII). The increase in DNA-P concen- 

 tration per unit PN in all cases of dietary deficiency, except that of vitamin 

 Bi2 , is an expression of the loss of protein from the cells without a loss of 

 DNA-P. According to Campbell and Kosterlitz^o the ratio of PN /DNA-P 

 varies linearly with N intake within certain limits of total food intake. 



The PNA-P per unit PN is rather more variable in its behavior. It would 

 appear that the synthesis or replacement of PNA and protein can be un- 

 coupled in dietary deficiencies, the loss of protein taking precedence in 

 protein"' ^^' ^^* and vitamin C deficiency,^^^ and the failure to replace PNA 

 predominating in cases of high fat diet," vitamin B12 ,^^ and thiamine de- 

 ficiency." The generalization suggested by Fukuda and Sibatani,^^ that 

 "in liver rapid accumulation or loss of protein lags behind the corresponding 

 rise or fall in PNA," would from the evidence reviewed above apply only to 

 variations in the intake of carbohydrate, fat,^^ and the vitamins B12 and 

 thiamine. When the diet is deficient in protein or vitamin C, the protein 

 loss from the liver exceeds that of PNA. 



VII. Neoplastic Tissues and Chemical Carcinogenesis 



In certain respects the composition of neoplastic tissue is much more uni- 

 form than that of normal tissues. Greenstein"^ stresses the strong resem- 

 blance between the chemical pattern of different tumors, and Potter et aU^'^ 

 have developed the concept that "normal cells may be converted to cancer 

 cells by the deletion of enzymes that are not essential for the life of the 

 cell." The similarity in the content of nucleic acids in tumor tissues of dif- 

 ferent origin was noted by Schneider,!^^ and this conclusion is supported 

 by the results collected in Tables VIII and IX. For nearly all the tumor 

 cells, and for liver tissue in a precancerous state after administration of 

 chemical carcinogens, the PNA-P/DNA-P ratio is greatly reduced and, in 

 many cases, is in the region of 1 or less. 



Cytochemical studies involving the direct observation of the cells in 

 fixed sections often show increased concentrations of PNA in hepatoma 

 cytoplasm in comparison with cells of adjacent healthy tissue. ^^^^ ^^^ Stow- 

 elP"^ reported more DNA per unit volume and per cell in most of the tu- 

 mors he studied. Although quantitative chemical determinations have borne 



1" J. P. Greenstein, "Biochemistry of Cancer," p. 367. Academic Press Inc., New 



York, 1947. 

 160 V. R. Potter, J. M. Price, E. C. Miller, and J. A. Miller, Cancer Research 10, 28 



(1950) . 

 1" W. C. Schneider, Cold Spring Harbor Symposia Quant. Biol. 12, 169 (1947). 

 '62 T. Caspersson, "Cell Growth and Cell Function." Norton and Co., New York, 



1950. 

 1" R. E. Stowell, Cancer 2, 121 (1949). 

 1" R. E. Stowell, Cancer Research 6, 426 (1946). 



