SEXUAL ACTIVITY OF MALE RABBITS A477 
of significance in reducing the sperm counts made upon the 
same. 
The averages of all the readings made from all the males at 
each service have been determined, and they show an unmistak- 
able downward trend, except that, on account of two unusually 
large figures in the 20th, the decline from 15th to 20th is less 
marked than in the other cases. However, as measured by the 
criterion of three times their standard deviations (with this irreg- 
ular data the use of the customary probable error is certainly not 
justified), the differences between contiguous means are without 
significance except in the case of that between the means for the 
Ist and 5th. The differences between the means of the 5th 
and 15th or 20th are also certainly significant, but not that be- 
tween the 10th and 20th. On the whole the mathematical 
methods of examining the data indicate that heavy sexual use 
has no very grave effect upon the number of sperm per cubic 
millimeter. However, the marked lack of regularity in these 
data demands that caution be used in accepting the arithmetical 
constants derived from the data as reliable indices of significance 
of the means and the data as a whole. In such eases a study of 
the extended figures themselves may actually give a truer 
meaning of the facts than the usual statistical methods of analy- 
sis. There are 22 cases in table 2 where 2 or more counts were 
made within a single series of matings. In 16 of these there is a 
marked falling off in sperm content of the semen as the number 
of services increases; in three cases there is a tendency for an 
increase of like figures and in three cases there is neither a clear- 
cut upward or downward trend of the counts as service number 
increases. It seems to the writers that by reading across the 
horizontal rows, one after another, one is furnished with almost 
convincing proof that there is a well-marked reduction in number 
of sperm per cubic millimeter in the advanced services. 
MOTILITY 
Motility of sperm cells has attracted as much or perhaps greater 
interest than the matter of their number. Motion is effected 
largely by a rapid vibration of the tail piece, but in some cases 
it appears that a spiral rotation of the entire body may aid 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 25, NO. 2 
