A76 ORREN LLOYD-JONES AND F. A. HAYS 
former he gives the specific gravity 1.0116 (average of 7 speci- 
mens) for the latter 1.035 (average of 9 specimens). It is prob- 
able that the specific gravity of rabbit semen is slightly greater 
than 1.0, and that the figures as published here represent slightly 
less than the true number of sperm per cubic millimeter. 
Table 2 presents the numerical data on sperm content obtained 
in this experiment. There are a great many gaps in the table and 
the observations seem badly scattered. This is the result, not of 
erratic methods, but of the vicissitudes and uncertainties of the 
work. Oftentimes the males would be used up to the 10th or 
15th mating and then the female which had given signs of heat 
would refuse the service. This was the most usual cause of 
failure to carry the series through to the limit. Again the male 
(especially the case with No. 3) would fail to proceed with the 
series as planned. When there are intervening spaces, such, for 
example, as with female No. 1, January 1, where records are 
given only on the Ist and 20th services, the cause of failure to 
make the readings complete was generally due to one of four 
causes, a lack of sufficient number of females in heat, the re- 
covery in the semen of urine, of blood, or of perceptible amounts 
of vaginal or uterine secretions which we had not succeeded in 
removing before service. 
The figures obtained, moreover, show wide and apparently 
capricious variations. For example, in the case of male No. 1, 
consider the mating on June 29, 1917. After 11 days’ rest the 
numbers on the Ist and 20th services are 140,000 and 8,000, 
respectively. On July 9th, after another rest interval of about 
equal length (10 days), the corresponding numbers are 230,000 
and 700. In each case the number at the 20th is greatly re- 
duced, but there is yet a strange lack of harmony in the relation 
of the numbers for the Ist and 20th services. This somewhat 
erratic nature of the data may perhaps in a measure be consid- 
ered as due to the variations in mood and condition of the males, 
but doubtless in larger measure to the unavoidable imperfections 
in our methods of recovery of the semen and to the small amounts 
of the same. That is to say that quantities of female secretions 
so slight as to be by themselves non-recoverable by catheter, 
might, when recovered with such small quantities of semen, be 
