138 PROBLEMS OF FERTILIZATION 



sperm suspensions of different concentrations it is 

 found that sperm suspensions of 1/240,000 per cent 

 decline to zero in their fertilizing power in about six 

 minutes, those of 1/30,000 per cent in about sixteen 

 minutes, those of 1/300 per cent not until after more 

 than two hours, while i per cent sperm may maintain 

 fertilizing power for two or more days. 



At the time when sperm suspensions are losing their 

 fertilizing power one can observe the phenomenon 

 described by Schiicking and Glaser at the proper 

 concentration of sperm. Thus in one of the writer's 

 experiments eggs were added to a 1/128 per cent sperm 

 suspension that was on the point of complete loss of 

 fertilizing power. In ten eggs selected at random an 

 average of nine spermatozoa was counted in the jelly 

 in an optical section. The spermatozoa were still 

 active, but the eggs did not fertilize. 



Gemmill (1900) observed a relation between dura- 

 tion of fertilizing power and concentration of sperm in 

 the sea urchin and concluded that the more rapid 

 exhaustion of spermatozoa in dilute suspensions is due 

 to dilution of a hypothetical nutritive medium which 

 keeps the spermatozoa of concentrated suspensions in 

 a vigorous condition. This explanation is not only 

 purely hypothetical but comes back to the principle 

 of loss of motility, which, as we have seen, cannot apply 

 in this case. 



The writer therefore holds that spermatozoa tend 

 to lose their fertilizing substance in proportion to dilu- 

 tion, so that they may thus become ineffective, whatever 

 their motility. For reasons discussed later it seems 

 probable that this fertilizing substance is identical with 



