EFFECTS OF RAYS OF RADIUM ON PROTOPLASM 341 



in the spindle in which the dividing egg chromosomes are located. 

 In my experiments, which are the reverse of his, since only the 

 eggs are radiated, it is the egg nucleus that gives rise to the 

 chromatin masses. That they represent abnormal chromosomes 

 is probable, since the number of these bodies, added to the number 

 of normal chromosomes in any figure, gives the usual diploid 

 number. Evidently, therefore, only a portion of the egg chro- 

 matin has been injured severely enough to produce obvious 

 changes in appearance. 



The achromatic portion of the mitotic figure is normal in every 

 respect. The further stages of division are normal except for 

 the presence of the injured chromosomes which may lie any- 

 where in the spindle. Occasionally they go to the poles where 

 they may be seen still condensed at the telophase, when the other 

 chromosomes have already become vesicular. 



This brief description indicates that the effects of a short 

 radiation are very slight. There is little evidence that the 

 protoplasm has been injured. A longer exposure undoubtedly 

 would produce more marked injuries, but such an exposure is 

 difficult to make in view of the fact that sea urchin eggs are 

 extremely sensitive to overcrowding and to a prolonged stay 

 in small quantities of water, conditions which are necessarily 

 imposed during radiation. 



DISCUSSION 



The character of the response of protoplasm to radium radi- 

 ations depends on the nature of the protoplasm itself, and on the 

 intensity of the exposure. In regard to the first point little can 

 be said except that cells differ from each other in their suscepti- 

 bility, wholly apart from the fact that each cell varies in sus- 

 ceptibility during different phases of its own activity. It has 

 been pointed out that an exposure of thirty minutes to the beta 

 rays will bring about in the developing sea urchin changes which 

 are as pronouncd as those produced in Nereis after ninety 

 minutes exposure to rays of the same intensity. Some Protozoa 

 are entirely unaffected at the end of fourteen hours of exposure, 

 while others are killed in a shorter period. There is a similar 



