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 hi 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 hi 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 hi 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 hi 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 hi 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 hi 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 hi the lens-producing antecedents hi 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 



