486 MARIE A. IIIXRICHS. 



Cohn, '17, '18, has shown that sperm in dilute suspensions are 

 more active than in concentrated suspensions. Active cells are, 

 on the whole, more susceptible to injury by radiation than are 

 quiescent cells. (See Hinrichs, '24, '266.) 



Ultraviolet radiation is particularly suited for experiments of 

 this kind, as compared with chemical agents, because, 



(1) Exposures may be very short and still be effective. A 

 superposition of the effect of staling is thus impossible. 



(2) The possibility of carrying over into the normal egg, at 

 the time of fertilization, small amounts of injurious reagent is 

 absent. Results are clear-cut and more likely to be due to 

 ultraviolet radiation alone, uncomplicated by other factors. 



I wish here to express my thanks to Dr. R. S. Lillie for his 

 interest and help in the study of this problem. . 



Conclusions. (i) Further data are given on the normal loss 

 of fertilizing power in sperm suspensions due to dilution and 

 staling. These results are entirely in accord with the ones 

 reported by F. R. Lillie in 1915. 



(2) Ultraviolet radiation augments the rate of loss of fertilizing 

 power beyond that produced by time and dilution. 



(3) Dilute sperm suspensions lose their power of fertilization 

 earlier and more rapidly when radiated (and even without 

 radiation) than do the more concentrated suspensions. 



(4) The rate of loss of fertilizing power is roughly proportional 

 to the dosage of radiation. 



(5) The motility of sperm is impaired and cleavage is delayed 

 and abnormal. Development is differentially modified. (See 

 previous paper, Hinrichs, '266.) 



. {6) Ultraviolet radiation produces sperm agglutination. 



(7) Fertilizing power decreases more rapidly than does motility 

 in both radiated and nonradiated suspensions. 



(8) Fertilization is incomplete when normal eggs are fertilized 

 by radiated sperm, and may in some cases lead only to mem- 

 brane formation. 



(9) The loss of fertilizing power is probably due to the loss 

 from the sperm, by outward diffusion, of some substance neces- 

 sary for fertilization. Ultraviolet radiation augments the loss of 

 fertilizing power, presumably by altering the surface of the 



