88 CHARLES PACKARD 



radiation of the egg produces a greater injurious effect than that 

 of the sperm. In early cleavage susceptibility of the cells is 

 increased, but in later stages he found, in common with many 

 other observers, that the susceptibility is greatly diminished. 



A more critical examination of the effect on the embryo of 

 radiating the germ cells has been made by O. and G. Hertwig who 

 also used the frog as a basis of investigation. In four series of 

 experiments they exposed first the fertilized eggs (A series) ; the 

 sperm (B series) ; the unfertilized egg (C series) ; and both eggs 

 and sperm before fertilization {D series). In general they found 

 that the exposure of the egg or sperm alone produced smaller 

 abnormalities than the exposure of the fertilized egg. In 

 the A series and in the D series the development was affected in 

 proportion to the length of exposure and the intensity of the 

 radiation. The same is true, up to a certain point, for the B and 

 C series. But if the sperm or the egg is exposed for a long time 

 the resulting embryo is fairly normal. In such cases, according 

 to O. and G. Hertwig, development is parthenogenetic, since the 

 sperm nucleus never becomes a part of the cleavage nucleus, but 

 serves merely to initiate development. The same is true when 

 the egg is radiated. The sperm nucleus and not the egg nucleus 

 is active. 



The embryos developing after the various types of treatment 

 show characteristic abnormalities. Gastrulation may be very 

 abnormal and the older embryos much bent, as described by 

 Schaper ('04). The internal structures also show great changes. 

 Most seriouslj^ affected is the nervous system in which the cells are 

 abnormal and the nuclei broken into granules. The blood system 

 also is injured. Physiological abnormalities are as marked as 

 the morphological. Growth is greatly retarded, due to the slow 

 rate of cell division. Though the muscles develop they are 

 paralized for lack of an adequate nervous system. The nuclear 

 disturbances in the affected cells are similar to those found by 

 earlier investigators, but the plasma of the cells appears to be 

 unchanged. 



A further study of the exact nature of the injury to the nucleus 

 has been made by P. Hertwig ('11) and G. Hertwig ('12). The 



