EFFECTS OF RAYS OF RADIUM ON PROTOPLASM 327 



MATERIAL 



The eggs of Nereis limbata and Arbacia punctulata were used 

 almost exclusively in these experiments. Some work was 

 also done on Drosophila ampelophila and on Paramoeeium 

 caudatum. 



OBSERVATIONS ON LIVING MATERIAL 

 a. The gamma rays 



With the apparatus employed it is difficult to determine what 

 percentage of the radiations falling on the shelf B is in the form 

 of gamma rays and what is in the form of secondary beta rays. 

 But whatever may have been their nature it is evident that they 

 produce a slight acceleration in the rate of cell division. This 

 is most marked in the eggs of the sea urchin, which were exposed 

 either before fertilization or immediately afterward. Text 

 figure 2 indicates the change in division rate. It is seen that the 

 first indication of cell division appears about 15 minutes before 

 a similar change occurs in the control. This difference is con- 

 tinued in the second cleavage. There is no abnormality in the 

 mode of division and the larvae develop with perfect regularity. 

 The acceleration is not cumulative; the eggs do not divide at 

 shorter and shorter intervals. After a few divisions it is impossible 

 to say whether the acceleration persists or not. 



Nereis eggs do not respond at all to the gamma rays. 



The eggs and larvae of Drosophila are not affected appreci- 

 ably by the gamma rays. The rate of growth is not changed 

 and the adults are fertile. 



Paramoeeium is not affected even by long exposures. Indeed 

 I have not been able to see any sign of abnormality or change 

 in the rate of division even after prolonged radiation with both 

 beta and gamma rays. This has been the general result reached 

 by other investigators on Paramoeeium. 



In order to test the effect of the gamma rays acting at a dis- 

 tance I placed the glass cells holding the material 5 cm. above 

 the radium. When the electro-magnet was in operation -the 

 beta rays were entirely deflected so that only pure gamma rays 



