28o ANIMAL AGGREGATIONS 



the original testicular fluid. The greater the dilution the greater is 

 the initial activity of individual sperm; but as dilution increases, the 

 effect on activity is less marked. In very dilute suspensions the ac- 

 tivity of a spermatozoon is more or less independent of dilution, but 

 in stronger suspensions the activity is much affected by further 

 dilution. That the reduced activity in strong suspensions is not due 

 to lack of O2 is shown by the fact that in one of Gray's standard 

 6 cc. of a suspension containing 25 mg. nitrogen' equivalents of 

 sperm, there is actually less O2 consumption than is shown by the 

 same volume of a suspension containing 5 mg. nitrogen equivalent; 

 and also by the fact that strong aeration failed to increase activity. 



Gray's interpretation is that inactivity of sperm in concen- 

 trated suspensions is due to lack of free space. Over a considerable 

 range of dilutions the specific activity of a spermatozoon is a linear 

 function of the cube root of the volume of sea-water. The total 

 initial activity is proportional to the number of sperm and to the 

 average free space for each cell. The initial degree of activity is 

 thus lower in the less diluted suspensions; but, interestingly enough, 

 the total energy expended during a period of at least 2.5 hours is 

 also distinctly less. The relation between density of spermatozoa 

 and rate of oxygen consumption may be accurately expressed by the 

 same formula used by Pearl to show the effect of population density 

 of the rate of reproduction in DrosopJiila (Pearl, 1925). 



Gray states, without supporting reference or evidence, that mu- 

 tual inhibition of activity of unicellular organisms is known among 

 the Protozoa, and particularly with Paramecia. The decreased ac- 

 tivity with massed spermatozoa may be the result of inhibitions due 

 to continual collisions, or it may be comparable to the effect of 

 thigmotactic reaction to foreign bodies in Paramecia. The behavior 

 of spermatozoa almost suggests a voluntary phenomenon in which 

 contractile effort is proportional to free space in which the organism 

 can move. Until more is known of the mutual effect of one cell 

 upon its neighbors, the phenomenon which Gray calls "allelostasis," 

 that is, the mutual depressing effect of one cell upon another, must 



' Total nitrogen present is used as a measure of sperm concentration. Oxygen con- 

 sumption is used as a measure of activity of sperm in suspension. 



