EFFECTS OF RAYS OF RADIUM ON PROTOPLASM 339 



never haploid, and the egg nucleus always develops, though 

 abnormally, through the maturation periods. It is impossible 

 to inhibit completely the activity of the egg nucleus without 

 destroying the entire egg. 



2. Experiments on Arhacia. A cytological study of Arbacia 

 eggs, radiated both before and after insemination reveals the 

 fact that the treatment produces very slight effects on the cell 

 constituents. Clear cut abnormalities such as were abundant 

 in Nereis are here very rare. Indeed it is only by careful search 

 that they can be found. This does not signify that radium is 

 incapable of effecting marked cytological changes in sea urchin 

 eggs, but merely that the treatment given in these experiments 

 was not severe enough. But inasmuch as abnormal develop- 

 ment always follows prolonged radiation, it is evident that pro- 

 found changes have taken place which cannot be rendered visible 

 by the technical means now at hand. The amount of visible 

 injury cannot be considered an index to the actual condition of 

 the cell constituents. 



The eggs were exposed for varying times to the gamma rays, 

 the rapid beta rays, and to a mixture of the rapid and slow type. 

 In those eggs treated with the gamma rays there is no sign 

 whatever of injury. As stated before, the only effect of such a 

 treatment is seen in the slight acceleration of cell division. 

 Exposure to the rapid beta rays likew'se produces no visible 

 cytological changes, but only a marked retardation in the rate 

 of development. When both slow and rapid beta rays are 

 utilized some effect on the cell constituents can be seen. 



Unfertilized eggs were exposed for 50 to 60 minutes to all the 

 available beta rays, after which they w^ere inseminated in finger 

 bowls. In each experiment a parallel series of exposures was 

 made on a very few eggs. Such a control is necessary since 

 overcrowding of the eggs frequently produces the same abnormali- 

 ties as the radium. By having two controls for each experiment 

 the danger of drawing false conclusions was minimized. In 

 the experiments to be cited there was always a sharp distinction 

 between the behavior of the radiated and the control eggs. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 19, NO. 3 



