RADIATION AND ARBACIA GERM CELLS. 465 



These experiments with sperm add further evidence for the non- 

 specificity of susceptibility relations along the egg axis, since the 

 characteristic difference in susceptibility is shown when the 

 radiation acts directly on the egg protoplasm as well as when 

 radiated sperm is used in place of normal sperm to fertilize the 

 normal egg. On the one hand, there is a differential susceptibility 

 to radiation, and on the other, to the action of radiated sperm. 

 The response on the part of the egg protoplasm is the same in 

 both cases, a differential inhibition, recovery, or acclimation. 

 Although we find a difference in the degree of susceptibility to a 

 given dosage of radiation, when we compare the fertilized egg, 

 the unfertilized egg, and the sperm, in general we find that the 

 resting unfertilized egg is less susceptible to a given dosage than 

 the sperm before union with the egg, or than the egg when 

 exposed immediately after union with the sperm. 



The action of radiation on the sperm is shown by the reduction 

 and frequent loss of motility (see also Lillie and Baskervill, 

 *22a), as well as by the interference with normal cleavage and 

 development. When stronger doses of radiation are used, the 

 fertilizing power is also reduced. (See later paper for fuller 

 discussion.) 



The differential effects produced by fertilizing normal eggs with 

 stained sperm previously exposed to sunlight or to diffuse day- 

 light are probably referable to a summation effect of "staling" 

 superposed on injury by radiation. In such experiments the 

 exposures often exceeded 30 minutes or even an hour, so that 

 although the sperm was highly concentrated when exposed, there 

 was probably a slight falling off in normal fertilizing power 

 during that period. 1 (See F. R. Lillie, '15, for study of effect of 

 time and dilution on fertilizing power of sperm.) 



These experiments were made at Woods Hole during the 

 summers of 1924 and 1925, and I wish to thank Dr. R. S. Lillie, 

 under whose direction the work was done, for his interest and 

 cooperation. 



Conclusions. From these results, further evidence is obtained 

 for the following: 



1 G. and P. Hertwig, '13 report two-hour exposures of the sperm of Sphcerechinus 

 and Slrongylocentrotus to the action of chloral hydrate, methylene blue, etc. 

 A two-hour delay in the use of Arbacia sperm results in considerable loss of ferti- 

 lizing power, even under normal conditions. 



