32 EFFECTS OF /3-RAYS OF DIFFERENT VELOCITIES 



separated the i3-rays, observed certain differences in their effects 

 upon the eggs of Arhacia and Nereis, but in this investigation no 

 attempt was made to compensate for the differences in intensity of 

 the rays to which the cells were exposed. ^ Congdon compared the 

 effects obtained by exposing seeds to a primary beam of /3-rays with 

 the effects of the same beam plus the soft rays, which were scattered 

 back from the primary beam from a surface of lead, and concluded 

 that in proportion to their energy content the slower rays have a 

 greater retarding action than the more rapid rays.^ 



The development of a method of measuring the physiological 

 action of radiations from radium has enabled us to examine the 

 problem quantitatively. The method depends upon the fact first 

 observed by Packard that the fertilization membranes of the eggs 

 of the marine worm, Nereis limbata, are greatly enlarged if the eggs 

 have been exposed to radium prior to fertilization.^ We have shown 

 that the extent of this change is a reliable measure of the intensity 

 of radiation.^ When used as instruments for measuring the strength 

 of a beam of heterogeneous rays, the eggs will take account of each 

 ray only in as far as it is effective physiologically. We have shown 

 that the influence of the 7-rays upon these eggs is negligible when 

 compared to the /3-rays,^ and have consequently neglected their 

 consideration in interpreting our experimental results. The general 

 plan of the investigation has been to expose Nereis eggs to approxi- 

 mately homogeneous beams of /3-rays of various velocities, to com- 

 pare the effects so produced with the effects produced on eggs from 

 the same worm by a heterogeneous beam of /S-rays of known intensity, 

 and in this way obtain a measure of the relative physiologically effective 

 radiation in each homogeneous beam. These values have then been 

 compared with the relative strengths of each homogeneous beam as 

 measured by their abihty to ionize air. Before going into the details 

 of the experiments it may be stated that they indicate that the ratio 

 of the physiological effect and the ionizing power of |3-rays is constant 

 for all velocities. 



^ Congdon, E. D., Arch. Entwcklngimechn. Organ., 1912, xxxiv, 267. 

 « Redfield, A. C, and Bright, E. M., Am. J. Physiol., 1917-18, xlv, 374. 

 ' Redfield, A. C, and Bright, E. M . , 7. Gen. Physiol., 1919-20, ii, 25. 



