ARE ACQUIRED CHARACTERS HEREDITARY? 341 
As already stated, once the anomaly is secured it may be trans- 
mitted to subsequent generations through breeding. So far we have 
succeeded in passing it to the eighth generation without any other than 
the original treatment. The imperfection, indeed, tends to become 
worse in succeeding generations and also to occur in a proportionately 
greater number of young. Though not analyzed completely as to its 
exact mode of inheritance, it has in general, the characteristics of a 
Mendelian recessive. Like such anomalies as brachydactyly or poly- 
dactyly in man, the transmission is not infrequently of an irregular, 
unilateral type, sometimes only the right, at others only the left eye 
showing the defect. In the later generations, probably in some 
measure as the result of selective breeding, there is an increasing num- 
ber of young which have both eyes affected. 
To determine whether the reappearance of the defect was due 
merely to the passing on of antibodies or kindred substances from the 
blood stream of the mother, or to true inheritance, we mated defective- 
eyed males to normal females from strains of rabbits unrelated to our 
defective-eyed stock. The first generations produced in this way 
were invariably normal-eyed, but when females of this generation 
were mated to defective-eyed males again, we secured defective-eyed 
young after the manner of an extracted Mendelian recessive. It is 
obvious that in such cases the abnormality could only have been 
conveyed through the germ-cells of the male, and that it is, therefore, 
an example of true inheritance. Subsequent matings have shown that 
these young transmit the eye-anomalies as effectively as do individuals 
of the original lines. A new strain of defective-eyed young, estab- 
lished about the time our original paper went to press, is also flourish- 
ing and, as regards transmission of the defect, seems to differ in no 
way from the earlier stock. 
But now, let us inquire as to where all this leads. Without enter- 
ing into a discussion of just what, serologically, is taking place in the 
body or in the germ of fetuses borne by the lens-treated mothers, the 
point I wish to emphasize is that a certain specific effect has been pro- 
duced; and, what is of greater moment, once the condition is estab- 
lished it may be not merely transmitted, but inherited. Whether the 
lens of the uterine young is first changed and then in turn induces a 
change in the lens-producing antecedents in the germ-cells of these 
young, or whether the specific antibody simultaneously affects the 
eyes and the germ-cells of the young is not clear. In any event it 
is evident that there is some constitutional identity between the 
