280 
L. L. LEWIS. 
credit them without further question, but over enthusiastic state¬ 
ments should not prejudice one against the study of the general 
question. Many breeders are successfully using artificial means 
of introducing the semen. The process is commonly called arti¬ 
ficial impregnation, but a better term would be artificial insemin¬ 
ation. The mere fact that the semen can be transferred success¬ 
fully by means of instruments has no value except as a matter of 
scientific interest unless there are practical reasons for attempting 
the work. A brief mention of the practical side of the question 
is of interest. 
The number of sperm cells present in the semen of a vigorous 
stallion will vary from one hundred and fifty thousand to two 
hundred and fifty thousand per cubic millimeter, and the semen 
from one service may vary from fifty to one hundred cubic 
centimeters. There may be as many as twenty-five billion of 
sperm cells present in the semen from one service. Since only 
one service of the cells is necessary for fertilizing the ovum, 
there is no reason, so far as numbers of spermatozoa is con¬ 
cerned, why a few cubic centimeters of the semen introduced by 
capsule or syringe would not serve the same purpose as direct 
service. 
Perhaps the point of greatest interest is the effect of contin¬ 
uous service on the number and vitality of the sperm cells. In 
one set of observations along this line the number of sperma¬ 
tozoa present at the beginning of the experiment was 131,000 
per cubic millimeter, with a vitality extending over nine hours. 
At the end of nine days, one service daily, the number of sperm 
cells per cubic millimeter was 5,800, and vitality continued for 
three hours. The horse used was a heavy, sluggish draft 
stallion. In another set of observations, where a vigorous young 
grade stallion was used, two services were given daily from 
December 14 to December 24, inclusive. The normal condition 
of semen for this horse showed about 200,000 sperm cells per 
cubic millimeter, and vitality of from eight to nine hours. A 
sample of the semen secured from the twentieth service showed 
23,000 sperm cells per cubic millimeter, with a vitality of not 
more than one and one-half hours. 
