May 15,1925 Possibility of Sex Control by Artificial Insemination 
901 
induce pregnancy. The young killed 
in this way, together with those which 
died in the first few weeks, make up 
about half of the total number pro¬ 
duced, and their sex was identified 
solely by autopsy. All young or par¬ 
tially grown rabbits which died were 
also autopsied to verify the records of 
their sex as determined from external 
examination. The ovary and testis 
have very distinctive shapes in the 
young rabbits even when just born. 
This is due largely to the distinct firm 
union of the epididymis to the testis 
and the small bulb where the epididy¬ 
mis curves at the anterior end of the 
testis as contrasted to the loose attach¬ 
ment of the Fallopian tube to the 
ovary. The positions of the ovary and 
testis are not so distinctive, for the 
testis is usually just starting to descend 
when the rabbit is born; but it descends 
in a very few days and, moreover, the 
gubernaculum testis is so prominent even 
at birth that it usually would serve for 
identification. Taken in connection 
with the shape and position of the 
testis, there is no room for doubt as to 
the sex of a young rabbit unless it has 
been partly eaten by the mother or 
has been dead long enough to have 
started to decompose. The female 
rabbit quite frequently eats her new¬ 
born young, and these, together with 
others about which the records are not 
quite clear, constitute the group of 
“unknown sex” in these records. 
MICROSCOPIC WORK. 
To parallel the breeding work with 
the rabbits and serve as a control by 
determining the effect of centrifuging 
upon the measurements of spermatozoa, 
smears were made of the untreated 
fluid just as it was recovered from the 
uterus or after dilution. Again after 
centrifuging there were smears made 
both of the “inside” and “outside” 
material and sometimes of material 
from intermediate positions. The ma-' 
terial was placed upon a clean slide or 
upon one which had been thinly coated 
with fresh albumen and was either 
heated first to fasten it to the slide and 
then was fixed in Bouin’s fluid or was 
fixed in Bouin’s fluid direct without 
any heating. As good results were 
secured without as with the heating, 
except that when the material had 
been much diluted there was sometimes 
not enough of its own protein to fasten 
it to the slide without heating and it 
washed off while being fixed in the 
Bouin’s fluid. The smears were stained 
in Heidenhain’s iron haematoxylin or 
in Delafield’s haematoxylin, with eosin 
as a counter stain. 
52205—251-2 
The head lengths of a large number 
of spermatozoa were measured on a 
number of these slides, but since this 
work necessarily requires a great deal 
of time only a small fraction of the 
whole number of slides made could be 
measured. The first measurements 
were made with a Spencer micrometer 
eyepiece, but all the later measure¬ 
ments were of drawings made with a 
camera.lucida, as this made it unneces¬ 
sary to touch the microscope tube at all 
during measurement and thus removed 
a possible slight error caused by jarring 
the tube when touching the microm¬ 
eter screw. However, when the ac¬ 
curacy of both methods was tested 
by measuring 100 spermatozoa twice 
the micrometer method was found to be 
slightly more accurate. The coefficient 
of correlation between first and second 
measurements was +0.671 ±0.037 for 
the camera lucida method and +0.761 
± 0.028 when the ocular micrometer was 
used. Seven hundred spermatozoa 
were measured on each of four normal 
slides, two containing the outside 
centrifuged and one the inside centri¬ 
fuged liquid. The “inside” slide, one of 
the “outside” ones, and one of the 
normal ones were all made from the 
same sample of recovered liquid. 
Microscopic work was also done on 
swine spermatoza to determine the ef¬ 
fect of centrifuging. Smears were 
made, in the same way as described for 
the rabbit, of the normal material and 
also of the material as taken from 
different positions in the centrifuge 
tube immediately after centrifuging. 
Measurements were made entirely by 
the camera lucida method of 700 
spermatozoa on each of three normal 
slides, three “inside” slides and one 
“outside” slide. 
VITALITY OF SPERMATOZOA 
A number of observations were made 
upon the effect of heat and cold upon 
the length of time spermatozoa re¬ 
mained motile. A bull was killed and 
the testicle was immediately removed 
and placed in a refrigerator and ex¬ 
amined daily afterward by making a 
fresh cut in the epididymis and look¬ 
ing for motile spermatozoa in the 
liquid which oozed out. A few motile 
spermatozoa were still found on the 
eighth day, but through an oversight 
all the ice was allowed to melt away 
that afternoon and on the ninth day 
the odor of putrefaction was' quite 
marked and no motile spermatozoa 
could be found. In the course of the 
work on the swine and rabbit sperma¬ 
tozoa the liquids were often kept in a 
test tube at temperatures varying 
