SEXUAL ACTIVITY OF MALE RABBITS 485 
that a temperature of 100°C. is fatal to the sperm. The length 
of time that sperm will retain its motility is largely decided by 
the temperature at which it is held. Lewis found that sperm 
from the horse retained motility about twice as long as 1 °C. 
as at 30°C. Payne (14) held sperm from cock birds at 34° F. 
and 106° F., and found that those at the former temperature dis- 
played motility three times as long as the latter. Puiersol (’93) 
kept human sperm at 3°C. and ca. 35°C. The former showed mo- 
tion at the end of nine days, the latter had ceased moving long 
before. Therefore, in order properly to interpret observations 
on duration of motion, it is essential that temperature at which 
observations were made be reported. 
In general it may be said that duration of motion is coincident 
with duration of life of the sperm, but this is not always true. 
At low temperatures, of course, contractile motion ceases, but 
returns upon warming. Stigler’s (’14) results also show that high 
temperatures also cause cessation of motion, which may return 
on cooling. In one case (Versuch, ’45) he repeatedly raised 
(45.5°C.) and lowered (room temperature) the temperature of a 
specimen of semen, thus causing repeated cessation and return 
of motion in the specimen. Hensen (’75) reports some very 
remarkable results which he obtained in inducing action in 
sperm which has ceased moving, by application of NaOH and 
KOH solutions. It is probable also that sperm which appear 
motionless under the microscope may be activated when placed 
within the female genital tract. 
Observations on the effect of heavy sexual service of the male 
on the duration of motion of sperm produced by him are few. 
Lewis (11, p. 30) allowed a heavy draft stallion to make nine 
consecutive services on as many days. This he considered heavy 
service for the stallion in question. The results of this series of 
services on the sperm content of the semen has been discussed. 
In the semen from the first service 20 per cent of the sperm were 
alive after 9.5 hours. In the case of 5th service all cells were 
dead at 9 hours. In case of 6th service 5 per cent were alive 
after 5 hours, but in the 9th service no cells were alive after 4.5 
hours. (All observations at 21°C. to 23°C.) Lewis also offers 
