30 I. LESLIE 



this out for the concentration of DNA, they reveal that the actual PNA 

 concentration per unit weight does not change appreciably or consistently 

 in most tumors (Tables VIII and IX). 



All tumors, however, are characterized by a decrease in the amount of 

 PNA per cell or in the amount of PNA relative to DNA. There is also a con- 

 sistent increase in the concentration of DNA-P per unit PN, indicating that 

 tumor or precancerous cells contain relatively less protein than the cor- 

 responding healthy cells (Tables VIII and IX). 



Different chemical and histological patterns are observed in liver tissue 

 during the induction of hepatoma by (a) carcinogenic azobenzene deriva- 

 tives and (b) N-acetyl-2-aminofluorene (AAF). The relative carcinogenic 

 potencies of some of the azobenzene derivatives are as follows : 4-aminoazo- 

 benzene (4-AB) and 2'-methyl-4-dimethylaminoazobenzene (2'-Me-4-DAB) 

 are noncarcinogenic; on the other hand, the relative carcinogenic activity 

 of 4-DAB is 6, and that of 3'-methyl-4-DAB (3'-Me-4-DAB) is 10 to 12. i^" 



For the first 8 weeks on a diet containing 3'-Me-4-DAB, there is no in- 

 crease in liver size, but a large increase in the concentration of DNA and 

 in the number of nuclei per unit volume of tissue. ^^^ According to Striebich 

 et al}^^ the same carcinogen increases the number of nuclei per gram of liver 

 two and a half times but decreases the mitochondria per gram by 40 % in 

 the preneoplastic liver. At the same time, the number of nuclei per liver is 

 doubled, and the number of mitochondria per cell reduced by one-fifth. 



The feeding of 4-DAB to rats over 5 to 6 months produced little or no 

 change in the total amounts and concentrations of liver protein, phospho- 

 lipid, and PNA-P, but their ratios to DNA-P were all greatly decreased." 

 In actual hepatomas, these ratios are half as great as in the control livers. 

 Although this change in composition corresponds to the picture of de- 

 creasing number of mitochondria described above, Schneider et al}^"^ claim 

 that this is true only of preneoplastic cells. In tumor cells, they find the 

 same number of mitochondria per cell as in normal cells, with the difference 

 that these mitochondria have "greatly altered biochemical properties." 



Laird^^- has described the dramatic change in liver cell population which 

 occurred between the twenty-sixth and twenty -eighth days of feeding rats 



1" A. C. Griffin, W. N. Nye, L. Noda, and J. M. Luck, /. Biol. Chem. 176, 1225 (1948) . 



»6« G. T. Mills and E. E. B. Smith, Science 114, 690 (1951). 



•" W. C. Schneider, G. H. Hogeboom, E. Shelton, and M. J. Striebich, Cancer Re- 

 search 13, 286 (1953). 



168 A. C. Griffin, H. Cook, and L. Cunningham, Arch. Biochem. 24, 190 (1949). 



159 J. M. Price, J. A. Miller, E. C. Miller, and G. M. Weber, Cancer Research 9, 96 

 (1949). 



'«" J. M. Price, E. C. Miller, J. A. Miller, and G. M. Weber, Cancer Research 9, 398 

 (1949). 



!«' M. J. Striebich, E. Shelton, and W. C. Schneider, Cancer Research 13, 279 (1953). 



i«2 A. K. Laird, Proc. Soc. Exptl. Biol. Med. 77, 434 (1951). 



