10 The Journal of Heredity 
when they first came into the season. 
Now if there were anything at all 
in the theory advanced that the time 
of mating controls the sex of the off- 
spring, a large proportion of these 
females must have performed in a 
nearly uniform manner, as all were 
under practically identical conditions 
or as nearly as possible to secure. 
“There were not two hens that per- 
formed in an identical manner, and 
there was not even an approximate 
uniformity in their performances. One 
hen produced all males, another pro- 
duced all females, and the rest, each 
seemed to take her own course in 
various degrees between these two 
extremes; some of the hens were mated 
again to the same male, and some to 
other males the following year, while 
some were discarded. 
“All those retained in the breeding 
pens the next year, regardless of the 
influence of the various males, repeated 
their former year’s work with some 
very slight variations. The hen that 
raised all females, after three years’ 
work, finally raised one cockerel, but he 
came after she had produced sixty pullets. 
“Five of her daughters were then 
tested and produced seventy-five pullets 
and two cockerels. In this family the 
sex tendency is strong enough to be 
transmitted, and in any family the 
individual that is strong enough to 
transmit his sex tendencies, certainly 
has greater power to transmit than 
the individual that cannot transmit 
sex tendencies and as a sire’s value 
depends on what he transmits, then 
the sire that transmits sex tendencies, 
especially a tendency to a predominating 
number of females, is of vastly greater 
value than the sire without this power 
or with a tendency towards a pre- 
dominating number of males. 
“Some one said: ‘Your bull may be 
losing $6,000 a year for you,’ but I 
know a whole family of bulls that 
carry world’s record blood in their 
veins that are putting their owners 
out of the dairy business at a rapid 
rate, not even suspected by their 
owners, and these bulls sold tor over 
a thousand dollars each.” 
The editor of Hoard’s Dairyman 
properly comments on this letter, that 
the amount of time through which 
Mr. Sharp’s breeding experiments have 
been carried is not enough to furnish 
conclusive proof. A breeding experi- 
ment well known to geneticists has 
been carried on for six years under the 
most careful conditions, however, and 
has given results which lend some 
color to the belief that one may get a 
strain of animals that has a tendency 
to produce disproportionate numbers of 
one sex. 
This is the inbreeding experiment of 
Dr. Helen Dean King at the Wistar 
Institute, Philadelphia, in which more 
than 22,000 albino rats have been bred 
and studied. Although Dr. King has 
not yet published her results, it is 
possible here to state the general trend 
of the experiment. 
In the rat, the normal sex ratio 
happens to be the same as in man and 
cattle, namely, 107 males to 100 
females. Dr. King began her work by 
taking from the stock animals one 
healthy litter of new-born rats, two 
males and two females. The descend- 
ants of one pair of the rats have, after 
the sixth generation, all come from 
the mating of brother and sister from 
litters in which males invariably pre- 
dominated. This is the A or male line. 
The B or female line of her experiment 
came from the other pair of the original 
litter and has been obtained by mating 
brothers and sisters from litters con- 
taining (after the sixth generation) an 
excess of females. In the first six 
generations no selection for sex was 
made, the object being to get the stock 
well-established and homogeneous. 
All of the 22,000 rats used are there- 
fore descendants of one or other of the 
two pairs in the litter first picked out 
for the foundation of the experiment, 
and in the two strains there has been, 
since the sixth generation, steady selec- 
tion in the opposite directions, through 
twenty-one generations, with strict in- 
breeding of the animals selected. 
By this process, the tendency to 
produce a disproportionate number of 
one sex appears to have been fixed in 
