EFFECT OF RADIUM ON CELL DIVISION 211 



STjnVIMARY 



Arbacia eggs exposed to a brief but intense radiation during 

 the period when the germ nuclei are approaching each other are 

 accelerated in their rate of cell division. Less intense radiation 

 produces less acceleration. 



Exposures made during the prophase result in an acceleration 

 unless they are prolonged, when a retardation ensues. 



During the metaphase the same phenomena appear but to a 

 greater degree. 



During the telophase the effects are much the same as in the 

 prophase. 



Eggs exposed during the resting stage are not easily affected. 



The power of the protoplasm and chromatin to absorb the 

 radiations does not change during these periods. 



The differences in the density of the chromatin during the 

 different phases of mitosis do not affect its absorptive power. 



During the metaphase when the eggs are most responsive to 

 radiations oxidations take place through the activity of enzjrmes. 

 If these enzymes are accelerated or retarded the effect is to 

 accelerate or retard the rate of cell division. 



Experiments indicate that radiations produce these effects on 

 extracted enzymes. 



It may be inferred therefore that the endoenzymes are af- 

 fected in the same way and that changes in the rate of cell 

 division, following radiation, are due to the direct action of the 

 radiations on them. 



THE JOURNAL OF EXPERI.M j:,XTAL ZOOLOGY, VOL. 21, NO. 2 



