484 MARIE A. HINRICHS. 



(See F. R. Lillie and Just, '24, p. 134.) Exposures up to 5 

 minutes produce but a slight immediate inhibition of motility; 

 exposures of 10-20 minutes produce a noticeable inhibition, while 

 exposures of 30 minutes completely paralyze the sperm. How- 

 ever, even after so long an exposure, a small percentage of the 

 eggs reach the 2- and 4-cell stage (less than I per cent.), but 

 proceed no further, suggesting that normal fertilizing power is 

 probably impaired before motility is lost. On the other hand, 

 shorter exposures (| min. to I min.) produce a marked reduction 

 of fertilizing power as measured by the percentage of eggs which 

 produce membranes and cleave. 



It seems probable that the loss of fertilizing power is due 

 rather to the outward diffusion of some substance necessary for 

 fertilization. Such a substance, if present at or near the surface 

 of the sperm, may easily diffuse into the medium by changes 

 induced in the sperm surface by surface-acting radiation. This 

 would result in the disturbance of the normal concentration 

 equilibrium of such a substance in the sperm which would then 

 become incapable of inducing normal and complete fertilization, 

 since the latter probably depends on an optimum concentration 

 of such a substance within the sperm. 



As before stated, highly diluted sperm suspensions are more 

 susceptible to injury than are the more concentrated suspensions. 

 Diffusion of sperm substance to the external medium following a 

 change in the permeability of the sperm surface induced by 

 radiation, would proceed more rapidly in dilute than in con- 

 centrated suspensions, since fewer sperm per unit volume of 

 suspension would contribute to the establishing of an external- 

 internal equilibrium. Diffusion of a. substance necessary for 

 fertilization, from the sperm into the medium may explain the 

 loss of fertilizing power induced by dilution and long standing. 

 It may also explain why more dilute suspensions are more 

 susceptible to an influence which is additive in its action on the 

 diffusion rate of such a substance. 1 



1 Compare the mass effects obtained by Robertson, '22, Drzewina and Bohn, 

 '21, '22. See also a later paper by Drzewina and Bohn, '230, for suggestion of 

 mass effect on sperm. Glaser's suggestion (Glaser, '15) of the necessity for the 

 presence of more than on* per egg in order to insure successful fertilization, 



may have some bearing on the problem of mass effects in sperm. 



