12 BULLETIN 905, TJ. S. DEPARTMENT OF AGRICULTURE. 
ing cells undergo specialization into skin, muscle, bone, nerve cells, 
etc., and never give rise to reproductive cells. The two classes of 
cells, reproductive cells and body cells, thus have separate histories, 
and any influence of one group on the other must be indirect. 
It will easily be seen that this leads to a very different conception 
of heredity from that mentioned above. The reproductive cells are 
not produced by the body. They are simply an unchanged bit of the 
same material which previously developed into the body of the 
parent. Heredity consists merely in their retention of the power 
to develop into a complete individual under the proper conditions. 
Thus, so far as heredity is concerned, the way in which an individual 
is related to his parents and more remote ancestors does not differ 
essentially from the kind of relationship with brothers, uncles, etc. 
This view of heredity was first reached by Sir Francis Galton, in 
England, and Augus l t "Weismann, in Germany, from a consideration 
of the history of the reproductive cells. Numerous experiments 
have also been made to test its truth. A striking illustration is 
given by an experiment performed by Prof. W. E. Castle and Dr. 
John C. Phillips, of Harvard University. They removed the ovaries 
of a female albino guinea pig and placed in her body the ovaries of 
an immature black female, aged about 3 weeks. The albino female 
was later mated with an albino male. Albinos, mated together, 
never produce any but albino young, a fact well known to all breeders 
of small mammals. Yet in this case, the young, six in number, 
were all black. These young were in three litters, born from 6 
months to a year after the operation. The immature ovaries of the 
black female were subject to the influence of the blood of the albino 
for from 4 to 10 months before the egg cells attained full growth and 
were discharged. Through it all they retained their original heredi- 
tary potentialities unchanged. 
MODIFICATION OF HEREDITY. 
Although the reproductive cells are not produced by the body, the 
possibility must be recognized that they may be modified in some 
cases by substances circulating in the blood. Recent experiments 
have, in fact, shown that changes can be brought about in the general 
vigor of the offspring in this way. Dr. C P. Stockard, of Cornell 
University, tested the effect of daily intoxication of guinea pigs 
with alcohol. The* animals themselves remained vigorous through- 
out the treatment. Their young, however, were markedh unthrifty 
compared with those of an unintoxicated control stock. This was 
true even when an alcoholic male was mated with a normal female, 
indicating that the reproductive cells of the male had been damaged 
by the alcohol. The injury seemed to be permanent, since a second 
generation produced by first generation animals, which had never 
