A. C. REDFIELD AND E. M. BRIGHT 29 



the average volume of a control of unradiated eggs was only 1.5 X 

 10^ cubic microns. This result would indicate that the 7-rays con- 

 tribute to the reaction of the Nereis egg. How small this contri- 

 bution must be, however, is indicated by the fact that an exposure 

 of about 1 1 minutes to 65 millicurie centimeters of /3- and 7-radiation 

 will produce an equivalent change in the membrane volume. The 

 7-rays alone require an exposure 60 times as long as the /3- and 7-rays 

 together. Inasmuch as long exposures to low intensities produce a 

 greater effect upon these eggs than short exposures to high intensi- 

 ties,'* the intensity of the physiologically effective /S-rays must be 

 much more than 60 times as great as the intensity of the physio- 

 logically effective 7-rays. 



SUMMARY. 



When Nereis eggs are exposed to radiations from a tube of radium 

 emanation, the walls of which absorb all the a-rays, the resulting 

 physiological change is produced by rays having a coefficient of 

 absorption of the order of 23.9 cm.~^ 



This fact indicates that the physiological effect is due almost 

 exclusively to j8-rays. 



The 7-rays alone can produce the reaction. To produce equiva- 

 lent physiological effects exposure to 7-rays alone must be approxi- 

 mately 60 times as long as exposure to ^- and 7-rays together. 



