70 



processes associated with growth just go on until the DNA finally doubled and the 

 cell was ready to divide? In such a case, you would have a larger than normal 

 cell by the time division was possible. 



I just put this out as a basis for not abandoning Tobias. 



BARRON: The lack of inhibition of protein synthesis and inhibition of 

 synthesis of nucleic acid was shown by Abrams in irradiated rats. 



MAZIA: The first diagram (Figure 6) shows the results of a series of 

 weighings of pairs of daughter amebae; that is, the two daughters resultingfrom 



2 16 



HOURS 



Figure 6^ Growth curves of Amoeba 

 proteus cells. Each pair of curves 

 represents the growth of sister cells 

 from the time of separation by division 

 of the mother cell until the time of their 

 division. Reduced weight is measured 

 by the Cartesian Diver Balance, and is 

 essentially the weight under water. 



PROPHASE- 



Figure 7. Interphase growth of 

 amoeba, showing course of changes in 

 reduced weight (proportional to dry 

 weight), volume, protein content, nu- 

 clear volume, and RNA content. 



a division were weighed immediately at 

 "birth" and their weights were followed 

 until they divided. The second diagram 

 (Figure 7) is a summary of various data 

 on the events taking place during growth 

 between divisions. The time scale is 

 slightly different because these data were 

 obtained on amebae grown under condi- 

 tions where the time between divisions 

 was longer than Z4 hours. These experi- 

 ments are made possible first of all, by 

 techniques that permit measurements on 

 single cells whose history is known and 

 secondly by a new technique of growing 

 cells in such a way that they divide syn- 

 chronously, thus permitting observations 

 on groups of cells of known history. 

 Data on the increase in "dry weight" dur- 

 ing the life of the cell are obtained by 



