May is, 1925 Possibility of Sex Control by Artificial Insemination 
895 
lay a very large number of eggs produced 
a much higher proportion of females 
than did the earlier ones. Jull (21, 
22), working with the domestic fowl, 
confirmed Riddle’s results as to the 
relation between reproductive over¬ 
work and the sex of offspring, but by 
making use of a sex-linked character 
in his breeding experiments Jull showed 
that all the males and females had the 
chromosome composition normal to 
their sex. This is added evidence in 
favor of the chromosome theory of sex 
determination, and the problem in the 
work of Riddle and of Jull becomes the 
discovery of what factor in the condi¬ 
tion of reproductive overwork governs 
the segregation of the sex-determining 
chromosome into the ovum or the 
polar body at the reduction division. 
Hays (16) obtained similar results with 
rabbits. 
There have been two notable success¬ 
ful attempts to establish, by selective 
breeding, strains which produce either 
an excess of females or an excess of 
males. The first of these was by 
Moenkhaus (30) working with Dorso- 
phila. He never succeeded in getting 
a strain which would produce a con¬ 
stant significant excess of males but 
did succeed almost from the start in 
getting a strain which averaged about 
75 males to 100 females. Warren (39), 
who repeated the same kind of experi¬ 
ment on a different strain of Droso¬ 
phila without success, showed that the 
results of Moenkhaus harmonized per¬ 
fectly with the idea that he was dealing 
with a strain which carried a sex- 
linked lethal factor, and since more 
than 20 such sex-linked lethal factors 
have already been found in Droso¬ 
phila melanogaster this case seems to 
support rather than to disprove the 
chromosome theory of sex determina¬ 
tion. The second successful attempt 
to establish excess-male and excess- 
female lines by selective breeding was 
that made by King (23), using albino 
rats. King’s results also conform fairly 
well to the hypothesis that her initial 
stock contained lethal factors. The 
results in the low male line fit the 
hypothesis that she was dealing with a 
strain containing a sex-linked lethal 
factor very well, except for the fact 
that the inbred females when bred to 
stock males produced a somewhat larger 
proportion of males than when bred to 
full brothers. The results in the high 
male line fit even better the hypothesis 
that she was dealing with a strain 
containing a sex-linked factor which, 
when homozygous, is lethal for females 
but has no effect upon males. (A 
similar factor has been reported (2) in 
Drosophila.) 
RELATION OF THE CHROMOSOME THEORY 
OF SEX DETERMINATION TO THE 
PROBLEM OF SEX CONTROL 
The existence of complete functional 
sex reversal is still in question even 
when considering birds and amphibians. 
Moreover, those cases which have been 
reported as proving such sex reversal 
in birds (9, 10, 35, 36) do not offer 
proof as to how such sex reversal might 
be controlled by the breeder. Further¬ 
more, Lillie’s work (24, 25, 26) on the 
freemartin has made it appear that 
complete sex reversal among the mam¬ 
mals is still more unlikely. Aside from 
the possibility of sex reversal, the 
problem of sex control may be ap¬ 
proached from two sides—either with 
the idea of destroying the fertilized 
eggs which are of the undesired sex, 
or with the idea of preventing the 
formation of such fertilized eggs. 
The work of Riddle (34), Jull (22), 
and Hays (16) may furnish a clue to 
some method of sex control, but as yet 
the underlying principles governing the 
partial success which they obtained in 
the control of sex have not been clearly 
demonstrated and have not been shown 
to be as completely susceptible to 
human control as would be desirable 
in a practical method of sex control. 
Killing or rendering impotent the 
spermatozoa which would produce the 
undesired sex seems to be a simpler 
method of attack, because treatment 
of the spermatozoa with a poisonous 
chemical agent could be in vitro, and 
the female could afterward be fertilized 
by artificial insemination. 
Separation of male-producing and 
female-producing spermatozoa by phy¬ 
sical means seems more possible than 
by chemical means. The physical dif¬ 
ferences upon which separation seems 
most possible are differences in motil¬ 
ity and differences in size. A differ¬ 
ence in motility might itself be due 
to a difference in size which would 
result in the smaller spermatozoa offer¬ 
ing less resistance to forward motion 
through the liquid by which they are 
surrounded. This is a possible explana¬ 
tion for the normal excess of males born 
among most species of mammals. In 
order to take advantage of differences 
in motility it would be necessary to 
keep the spermatozoa oriented in one 
direction. Possibly this might be done 
by means of an electric current, but, so 
far as the author knows, this has not 
been tried. A physical separation of 
the spermatozoa upon the basis of their 
size difference hardly seems possible 
by any filtering or straining method be¬ 
cause of their smallness and delicacy. 
However, separation of the two sizes 
