EFFECTS OF RAYS OF RADIUM ON PROTOPLASM 333 



In this respect the results differ from those of Paula Hertwig ('11) 

 who states that in Ascaris the only effect of radiation is on the 

 nucleus. With larger amounts of radium I have repeated the 

 previous experiments, and am able to confirm my former state- 

 ments in regard to Nereis. Experiments on the sea urchin tend 

 to confirm the observation of Miss Hertwig. This situation 

 illustrates the difficulty of making any general statement on the 

 effect of radium on protoplasm. In the following section I 

 will describe the changes brought about in the eggs of Nereis 

 and Arbacia by means of the rapid and slow beta rays. 



/. Experiments on Nereis 



The eggs develop in different ways depending on the nature 

 of the rays employed and on the length of exposure. In general 

 there are three fairly distinct types of development. The first 

 type is seen in those eggs which have been exposed to the rapid 

 beta rays at 50 mm. distance before insemination. The peri- 

 vitelline space is not increased in width; the sperm enters much 

 earlier than normal, and the maturation divisions, which are 

 normal, take place at a correspondingly earlier time. About 

 75 per cent of the eggs thus treated show this peculiarity. The 

 second type predominates when the unfertilized eggs are exposed 

 to the slow and rapid beta rays at 4 mm. from the source. The 

 perivitelline space is at first normal but after a short time in- 

 creases notably in width. The sperm enters early, as in the 

 preceding case, but the maturation divisions are abnormal. 

 Almost every egg is thus affected. The third type is seen when 

 the eggs are exposed to the rapid beta rays acting at 4 mm. dis- 

 tance. The perivitelline space, in about 75 per cent of the eggs, 

 is greatly extended; the sperm usually fails to enter, and the 

 maturation divisions are abnormal. 



The early entrance of the sperm is a very striking and con- 

 stant phenomenon. In table 1, which is a summary of several 

 experiments performed in different ways, the rate of entrance 

 and the subsequent phenomena of maturation and cleavage are 

 shown. The first column shows the normal course of develop- 



