May 15,1925 Possibility of Sex Control by Artificial Insemination 
897 
all and which is of cardinal importance. 
The second factor of success is the dif¬ 
ference, if any, in the specific gravity 
of the two classes of spermatozoa, 
which also is not under control and 
moreover is not readily ascertainable. 
The third and fourth factors are the 
specific gravity and viscosity of the 
surrounding liquid. These could be 
controlled within limits by the addition 
of water or of certain solutes, provided 
this was not carried so far as to injure 
the spermatozoa. A more serious 
difficulty in the way of controlling the 
specific gravity and viscosity of the 
liquid lies in the fact that the liquid as 
recovered from the vagina and uterus 
of the female by a catheter varies so 
greatly in those properties that it 
would be necessary to determine them 
anew for every sample. The fifth and 
sixth factors are the amount of centrif¬ 
ugal force used and the length of time 
for which it is applied. These are 
quite within the control of the experi¬ 
menter, but he has no way to determine 
the correct time or the correct force to 
use except by trial. Moreover he can 
only know whether he has succeeded 
by a microscopic examination (meas¬ 
urement) of the spermatozoa in samples 
from the inside and from the outside 
of the centrifuge, which would require 
a good many hours of continuous work 
and practically could not be carried 
out until the spermatozoa were too old 
to be viable, so that no advantage 
could be taken of the knowledge. It 
will readily be seen that the difficulties 
in the way of finding and maintaining 
the correct technique are very many 
and very serious, but nevertheless they 
did not seem insuperable. 4 
MATERIAL 
The rabbits used were of mixed stock, 
small or medium in size, derived largely 
from such varieties as the Black Dutch, 
New Zealand Red, Himalayan, and 
ordinary albinos and other colors of 
mixed ancestry. The advantages of 
the rabbit as material for work of this 
sort are that it is of very convenient 
size for operation and for artificial in¬ 
semination; that the period of gesta¬ 
tion is very short and the size of litter 
is large, thus permitting the production 
of large numbers in a very short time 
because the young can be killed at 
birth if their sex is the only point on 
which information is wanted; that 
they breed all the year (to some ex¬ 
tent, although more readily at some 
seasons); and finally, that they are 
rather cheaply maintained, and since 
they are mammals it is reasonable to 
suppose that principles learned from 
them would apply also to other domes¬ 
ticated mammals or to man. The dis¬ 
advantages of using the rabbit are that 
the females are quite subject to infec¬ 
tion of the uterus and Fallopian tubes 
by pus-forming bacteria and the differ¬ 
ence in size between the X-chromosome 
and Y-chromosome is not very great(I). 
The material from swine was ob¬ 
tained from three different Poland- 
China boars from the University of 
Wisconsin herd. Two of these were 
mature and one was about 10 months 
old. The two mature ones were cas¬ 
trated and the testicles, in the one case 
immediately and in the other case after 
immersion for about three hours in 
water at about 25° to 35° C., were 
opened with a knife and a milky fluid 
which oozed out from the many cut 
ends of the epididymis was collected by 
means of a catheter and a rubber bulb. 
The young boar was allowed to copu¬ 
late with a sow and the fluid which 
could be recovered from the sow imme¬ 
diately afterward with a catheter and 
rubber bulb was used for the micro¬ 
scopic studies. Swine are too slow 
breeding and too expensive to maintain 
for the carrying out of the actual breed¬ 
ing experiment unless there should be 
unusually good reasons to expect suc¬ 
cess with them. The chromosome com¬ 
position of swine as reported by Wodse- 
dalek {43) is such as to give more rea¬ 
son to expect success in the centrifugal 
separation of the two classes of sper¬ 
matozoa in this animal than in most, or 
perhaps than in any other which has 
yet been studied. It should be added 
that Hance {14) could not confirm 
Wodsedalek’s results. According to 
Wodsedalek, the male-producing sper- . 
matoza contain 8 and the female- 
producing spermatozoa 10 chromo¬ 
somes, and, as nearly as can be judged 
from his drawings, the 2 chromosomes 
which together behave as a single X- 
chromosome constitute 20 to 30 per 
cent of the volume of the chromatin 
in the spermatozoa which contain 10 
chromosomes—that is, the volume of. 
the male-producing spermatozoon 
might be expected to be 70 to 80 per 
* The work was done in the laboratories of the department of genetics at the University of Wisconsin. 
It was originally planned by and was continually under the direction of L. J. Cole. Some preliminary 
work by Sarah V. H. Jones and L. J. Bachhuber had indicated that mechanical separation of the male- 
producing and female-producing spermatozoa might be possible by means of centrifugal force, and there¬ 
fore that sex control would be possible by artificially inseminating the females with only the desired kind 
of spermatozoa. On the strength of this preliminary showing a detailed test of this possibility was made, 
using rabbits for the experimental animals but also making a few tests on Semen from swine. The micro¬ 
scopic work was done with the advice and assistance of M. F. Guyer of the zoology department. 
