May is, 1925 Possibility of Sex Control by Artificial Insemination 
911 
slightly that it is uncertain whether 
centrifuging effects a separation at all; 
certainly it is not a complete one, and 
the conditions under which each 
insemination and centrifuging are per¬ 
formed necessarily vary so much that 
the necessary adjustments of technique 
appear to be insurmountable difficulties 
to the successful control of sex in rab¬ 
bits by this method even though the 
theoretical basis of the method may be 
perfectly sound. 
The microscopic work on swine 
spermatozoa was directed toward an¬ 
swering the same two questions as was 
the work with the rabbits, but was 
unaccompanied by any breeding work. 
The first question, as to the existence 
of a dimorphism in the spermatozoa 
head lengths, has already been an¬ 
swered very positively by Wodsedalek 
(4-1).) and since the difference reported 
between the mean sizes of the two 
classes was so large it seemed that this 
was excellent material for seeking an 
answer to the second question. How¬ 
ever, the dimorphism revealed by the 
examination of untreated spermatozoa 
in this work was not nearly so distinct 
as that reported by Wodsedalek. 
Where the expectation is that the mean 
size of the larger kind will exceed that 
of the smaller kind by about 20 per 
cent, the actual results are that the 
mode of the larger kind is from 7.1 to 
8.6 per cent larger than the mode of 
the smaller kind. Just what is the 
reason for the difference in results is 
not clear. The material used is almost 
identical, the animals being of the same 
breed, from the same herd, and one at 
least being of the same age as the one 
used by Wodsedalek. The only differ¬ 
ence, aside from differences in staining 
and possible errors in measurement, is 
that the spermatozoa used in this work 
were mature spermatozoa from the 
epididymis of the testicles, or were 
already ejaculated, whereas Wodseda¬ 
lek measured spermatozoa in the 
tubules themselves, using as a criterion 
of their maturity the fact that they 
were in the lumen free from the sur¬ 
rounding tubule walls. 
However, it seems certain that a 
dimorphism of spermatozoa does exist, 
although it may not be as great as was 
first reported. All three of the curves 
of untreated spermatozoa show two 
modes, rather close together and of about 
equal height; all three are wider at the 
apex and narrower at the middle than 
the theoretical, and therefore, although 
the average figure for their goodness of 
fit is fairly high, it seems certain from 
inspection that they really are com¬ 
pounded of two overlapping curves of 
about equal frequency. 
The slides made from the centrifuged 
material agree in indicating that cen¬ 
trifuging tends to separate the smaller 
spermatozoa to the inside and the 
larger spermatozoa to the outside of 
the centrifuge tube, but that the separa¬ 
tion is not complete. All three of the 
slides made from the inside material 
are skewed to the left and the one made 
from the outside is quite strongly 
skewed to the right. The unusual 
shape of the curve from slide No. 526 
may be connected with the fact that it 
was made of material from the next to 
the extreme inside one-sixth of the 
centrifuge tube instead of the extreme 
inside, as slide No. 531 was. Slides 
519, 531, and 536 are made from the 
same material, and slides Nos. 522 and 
526 are both made from material from 
the younger boar. 
The conclusions which can be drawn 
from the work on swine spermatozoa 
are that there is a definite dimorphism 
in size, but that the difference between 
the two kinds of fully mature sperma¬ 
tozoa is probably not as great as was 
reported by Wodsedalek. Centrifuging 
effects a partial separation, throwing 
more of the large spermatozoa to the 
outside and leaving more of the small 
ones in the inside portions of the liquid. 
As pointed out in discussing the theory 
of centrifuging, this is the effect to be 
expected when bodies of varying size 
are suspended in a liquid which is 
slightly less dense than the bodies 
themselves, and that the spermatozoa 
are of a slightly greater density than 
the surrounding liquid is shown by the 
fact that the majority of the sperma¬ 
tozoa are thrown to the outside in 5 
minutes of centrifuging and almost all 
of them if the centrifuging is prolonged 
much beyond 10 minutes. 
Whether the separation is complete 
enough or the technique can be made 
simple enough so that sex control by a 
method based on these principles ever 
can be made practical in swine is still 
an open question. There does not ap¬ 
pear to be much economic advantage 
in being able to control sex in swine, 
but the scientific interest would be con¬ 
siderable. Even if it can be made 
practicable in swine, such a method 
would be restricted to animals in which 
the X-chromosome constituted a very 
large and the Y-chromosome a very 
small percentage of the total chromatin 
of the cell. That, of course, eliminates 
a large number of animals, including 
