MASS PHYSIOLOGY OF SPERMATOZOA 279 



Their effect can be neutralized by treatment with sodium citrate. 

 Gray suggests that these trivalent ions have this effect upon the 

 spermatozoa because of the electric charges carried by the former. 



Gray returned to a consideration of the whole problem of sperm- 

 suspension dilution in relation to functional longevity in 1928. He 

 repeated the well-known observations that as long as seminal fluid 

 of a ripe sea urchin remains undiluted, little or no movement occurs 

 on the part of the sperm. If a small drop of this fluid comes into 

 contact with sea-water, the cells at the surface at once become in- 

 tensely active, and eventually the whole lot of spermatozoa exhibits 

 lively movement. Gray suggests four possible causes: (i) There 

 may be an inhibiting substance in testicular fluid. (2) Sea-water 

 may contain some element absent from testicular fluid necessary 

 for movement. (3) The viscous resistance of testicular fluid may 

 be too high to allow movement. (4) Each spermatozoon may exert 

 some form of inhibition on the movement of its neighbors. 



If undiluted sperm be centrifuged, they can be separated from the 

 surrounding testicular plasma. If a drop of undiluted sperm be 

 added to this plasma so that it becomes diluted thereby, activity 

 results as in sea-water. Appropriate checks show that the results 

 are not due to changes in CO2 or O2 tension due to centrifuging. 

 Gray thinks, therefore, that the activating effect of dilution in sea- 

 water is due to mechanical dilution whereby each spermatozoon is 

 given more space, allowing free movement. The spermatozoa do 

 not move when closely packed; but what is more striking, they make 

 no effort to do so; this can be demonstrated by comparing O2 con- 

 sumption of undiluted and diluted sperm. As movement becomes 

 retarded in the diluted sperm due to increased CO2 tension, artificial- 

 ly produced, or to the passing of time, the rate of O2 consumption 

 approaches that of the originally undiluted sperm. In this connec- 

 tion it would be interesting to know if the same effect can be ob- 

 tained by diluting the sperm and then packing it together again in 

 sea-water with a low CO2 content. 



Except in very dilute suspensions the respiratory level at the 

 beginning of active life is not simply proportional to the number of 

 spermatozoa present, but also depends on the degree of dilution of 



