60 S. S. COHEN 



Allard et al. (1952a,b, 1953) have proceeded to the direct quantitation of 

 mitocliondria per cell. In Table V are presented some of their data on the 



TABLE V 

 Mitochondria Population of Eat Liver Cells" 



Mitchondria per cell IMitochondria per gm. liver X 10" 



Normal 2480 33.0 



Tumor 711 39.0 



Regeneration (2 days) 2089 25.7 



Semisynthetic diet 1940 26.7 



« Allard e< fl/. (1953). 



number of mitochondria per Hver cell of rats treated in various ways. It can 

 be seen that liver tumors which developed as a result of 4-dimethylamino- 

 azobenzene in the diet contained markedly fewer mitochondria per cell, 

 although the total number of mitochondria of tumor was higher than in 

 normal liver. ^ 



Similar problems concerning mitochondrial synthesis arise in normal 

 development. A diminution in mitochondrial number per cell occurs during 

 gastrulation in the sea urchin larva (Gustafson and Lenique, 1952); this is 

 found, in general, during growth unattended by differentiation. 



The apphcation of the principle of quantitating activity and subcellular 

 elements per cell promises to provide much information on the nature of 

 physiological and pathological change. Such methods have not yet been 

 applied to virus-infected cells. 



4. Biochemical Heterogeneity of Mitochondria 



Although isolated mitochondria exhibit similar staining and optical 

 properties, they are highly pleomorphic. It is conceivable that differences in 

 size and shape may reflect biochemical differences among the particles. 

 Density gradient techniques have been successfully used to effect separations 

 of classes of mitochondria on the basis of density differences (Ottesen and 

 Weber, 1955; Thompson and Mihuta, 1954). In the latter study, there also 

 appeared to be a separation of uricase from other mitochondrial enzymes, a 

 result noted by other groups using the more conventional differential centri- 

 fugation techniques (Kuff and Schneider, 1954). 



In a more recent study, however, with fractions collected by centrifugation 

 in a density gradient (Kuff et al., 1956), electron micrographs appeared to 



^ However, several other laboratories (Shelton et al., 1953; Fiala, 1953) report, follow- 

 ing mitochondrial counts and isolations, that even based on the weight of hepatoma and 

 normal liver, the latter contains about 2.5 times as many mitochondria as does hepatoma. 



