SEXUAL ACTIVITY OF MALE RABBITS 481 
between the deposit of the sperm and the time of its arrival in 
the upper tract cannot be used in reckoning the rate at which 
the sperm may move by virtue of its own motive power. 
The point on which the present work particularly bears is the 
influence on the rate of motion, of unusual sexual exercise by the 
male. Iwanoff has reported data which bear on this point. He 
(07, p. 494) mated a stallion which was known to produce sperm 
of great activity as follows: Beginning August 20, this stallion 
made two copulations, and August 23, four copulations at inter- 
vals of two hours. Sperm from the last three copulations showed 
very feeble motion (numerical data not given). Stigler (714, 
p. 219) states that Mantegazza obtained semen from a man one- 
half hour after a previous copulation and that the sperm in the 
same ‘mit viel geringer Energie bewegten.’ 
In making the counts given in this paper the semen was in all 
eases diluted with 9 volumes of Ringer’s solution. In undiluted 
rabbit semen the sperm are so crowded that a straight-ahead 
course can be pursued for only a very short distance and the 
motion is greatly impeded. Moreover, the varying viscosities 
of natural semens, as Lespinase (’17) states, serve as an external 
factor to modify the rate of motion. A drop of this diluted. semen 
was placed in the counting chamber of a haemacytometer. This 
instrument is very well suited for such readings because the 
graduations make the linear distance covered by the sperm easily 
determined and there is an abundance of free space in which the 
cells can move. The observations made on the ‘rate of motion’ 
of sperm were always made on individual sperm unencumbered 
by foreign bodies, showing the progressive vibratile type of 
motion. A stop-watch was used to determine the time required 
for a sperm cell to pass over from two to five or six 0.05 mm. 
spaces on the cytometer. This time interval was set down for a 
considerable number of sperm on the slide, an average of the re- 
sults was taken as the correct measure of motility and recorded 
together with the temperature of the liquid in which the sperm 
were moving. 
Temperature is of course a factor which has a most profound 
influence upon the rate of motion, and unfortunately this has 
