178 



SUBCELLULAR PARTICLES 



fed isotope for different times can be presented as a curve representing changes 

 in the relative specific activity of the RNA's of different structures. Table 2 and 

 figure 5 show data obtained in this way when larvae were fed food containing 

 adenine-8-C' '. In plotting the data for the nucleus the grain counts were multi- 

 plied by 2.37 to correct for difference in concentration; therefore, the curves rep- 

 resent relative changes in specific activity with time. For this experiment about 

 200 larvae hatched from eggs deposited during a 6-hour period were segregated 

 when about one-half of the larvae in the culture had moulted the second time. 

 By selecting only those in third instar a relatively uniform population was ob- 

 tained. They were placed on food containing the isotope and a red colored ma- 

 terial, carmin. Larvae were selected for the experiment only if they began eating 

 immediately when placed on radioactive food. Likewise when the larvae were 



Table i. Changes in cytoplasmic, nuclear and nucleolar volumes (cubic microns) of 

 sali\arv glands in early third instar larnae of dro:ophlla repleta 



Time (hours) 



-H I ' — 



Fig. 5. (Jraph sluiwin.u relative .specihc activities of RNA after feeding larvae of Drosophila 

 for 2 hours on ailenine-C". The points were calculated from grain counts in table 2. 



