158 



Fraction of interphase time 



Fig. 3. The DNA content of cells from mouse heart, growing in tissue culture. 

 DNA content was measured microspectrophotometrically on Feulgen-stained cells. 

 The number of cells on the ordinate contain the amount of DNA shown on the 

 abscissa. The lower curve was constructed from this distribution a.ssuming an 

 exi)onential rate of cell growth and that a constant amount (previously determined) 

 of the division cj^cle was devoted to interphase. (From Richards ct al., 1956.) 



ki.ss, 1954; Young and Fitz-James, 1959; Iwanmra, 1955; Earner and 

 Cohen, 1956; Lark and Maal0c, 1956; ]\Iaruyania, 1956; Scott and Chii, 

 1958; Maruyania and Lark, 1959; Foster and Stern, 1959; Newton and 



