472 ORREN LLOYD-JONES AND F. A. HAYS 
by the formula ot — y = Vox? + cy? where x and y represent 
two different means) are also set down. If an observed difference 
between two means exceeds three times the standard deviation 
calculated thus, then the difference can hardly be ascribed to 
fluctuations of sampling (Yule, p. 346, also 140, Ed. 1916). 
The means, to be sure, show a continuous decline, but the 
differences between no two contiguous means, as tested by 
the above principle, are significant. 
If we consider the differences in mean volumes between the 
Ist and the 15th service, however, we have a decrease for the 
15th which is certainly significant. The standard deviation 
for the difference between the Ist and the 15th means is 0.0420, 
only about one-fifth the difference between the means. The cor- 
responding figure for the 1st—20th is 0.0329 which is less than one- 
seventh of the difference between the means. In a very general 
way our data on volume of semen corroborate the work of others 
cited with the horse and with man, but it is not to be compared, 
in significance, with the results quoted on horse, man, and dog, 
in which cases, the entire discharge may be recovered and in 
which additions from the female tract may be avoided. 
CHANGES IN GENERAL PROPERTIES 
Certain changes in general properties of the semen occur when 
a number of coitus rapidly succeed each other. The semen 
becomes less viscous and tends to lose its characteristic milky 
appearance until at the 20th service the fluid recovered is fre- 
quently of a thin, watery nature. In other words, under con- 
tinued stimulation the glands which produce the semen not only 
show reduced activity, but the quality of their product is changed 
as well. This change in consistency and composition of semen 
due to excessive sexual activity has been recorded by other work- 
ers. Lode (’91) found that in the case of the dog there was a 
decrease in specific gravity of semen from 1.014 at the first 
ejaculation to 1.010 on the third ejaculation in a day, and 
Lewis (11, p. 37) reports a decrease in total solids after a stal-. 
lion had served twice daily for a number of days. 
