AUGUST WEI S MANN 339 



predisposition may be transmitted from father to son, in the form of 

 bony tissue with a more susceptible constitution. But I should deny 

 that the son could develop an '' Excrcicrknochen" without having 

 drilled, or that, after having drilled, he could develop it more easily 

 than his father, on account of the drilling through which the latter 

 first acquired it. I believe that this is as impossible as that the leaf 

 of an oak should produce a gall without having been pierced by a 

 gall-producing insect, as a result of the thousands of antecedent gen- 

 erations of oaks which have been pierced by such insects, and have 

 thus ^'acquired" the power of producing galls. I am also far from 

 asserting that the germ-plasm — which, as I hold, is transmitted as the 

 basis of heredity from one generation to another — is absolutely un- 

 changeable or totally uninfluenced by forces residing in the organism 

 within which it is transformed into germ-cells. I am also compelled 

 to admit that it is conceivable that organisms may exert a modifying 

 influence upon their germ-cells, and even that such a process is to a 

 certain extent inevitable. The nutrition and growth of the individual 

 must exercise some influence upon its germ-cells ; but in the first place 

 this influence must be extremely slight, and in the second place it 

 cannot act in the manner in which it is usually assumed that it takes 

 place. A change of growth at the periphery of an organism, as in 

 the case of an '' Exercierknochen," can never cause such a change in 

 the molecular structure of the germ-plasm as would augment the pre- 

 disposition to an '' Exercierknochen," so that the son would inherit 

 an increased susceptibility of the bony tissue or even of the particular 

 bone in question. But any change produced will result from the reac- 

 tion of the germ-cell upon changes of nutrition caused by alteration in 

 growth at the periphery, leading to some change in the size, number, or 

 arrangement of its molecular units. In the present state of our knowl- 

 edge there is reason for doubting whether such reaction can occur at 

 all ; but, if it can take place, at all events the quality of the change in 

 the germ-plasm can have nothing to do with the quality of the acquired 

 character, but only with the way in which the general nutrition is in- 

 fluenced by the latter. In the case of the '' Exercierknochcn" there 

 would be practically no change in the general nutrition, but if such a 

 bony growth could reach the size of a carcinoma, it is conceivable that 

 a disturbance of the general nutrition of the body might ensue. Cer- 

 tain experiments on plants — on which Nageli showed that they can be 



