MASS PHYSIOLOGY OF SPERMATOZOA 281 



remain obscure. This last explanation of the effect of dilution upon 

 spermatozoan physiology is fundamentally the same as Gemmil's 

 first assumption. 



It is a well-known fact that the fertilizing power of sperm falls 

 more rapidly when sperm are kept in dilute suspension than when 

 they are concentrated. The usual explanation is that in stronger 

 suspensions activity is inhibited by CO2 given off by the sperm, and 

 so the cells conserve their energy (Cohn, 1918). Gray's data show 

 that this explanation is only partially correct at best and may be 

 quite erroneous. In his experiments the CO2 product was continu- 

 ously removed, and the respiration per unit of sperm suspension in 

 the concentrated mass at no time equals that in the diluted sus- 

 pension. 



If the conditions of a dilute sperm suspension are such that the 

 CO2 generated is allowed to accumulate, the rate at which energy is 

 expended will decrease, which will tend to increase the length of 

 life during which the cells are motile when the CO2 is removed by 

 subsequent dilution. Such conditions appear to have existed in some 

 of Cohn's experiments where the suspensions were very dilute and 

 the full initial activity was mechanically possible. In such suspen- 

 sions it should be possible to show that the rate of respiration in 

 relation to the percentage of sperm was the same in all cases. 



Gray's conclusions are: 



1. Relative inactivity of undiluted Echinus sperm is not due to 

 physical and chemical constitution of their natural medium in the 

 testis, since the cells are intensely active in this mecUum when the 

 majority of the spermatozoa are removed by centrifuging. 



2. Total activity of any suspension, as measured by its O2 de- 

 mand, is proportional to the number of sperm present and to the 

 average space in which each cell is free to move. Inactivity in the 

 testis appears to be due to mechanical overcrowding, each cell ap- 

 pearing to exercise a restraining, or allelostatic, effect on the activity 

 of its neighbors. 



3. Total energy expended during life of sperm, as well as the 

 level of activity exhibited immediately after activation, depends on 

 the degree of dilution of the suspension examined. 



