170 THE CONTINUITY OF THE GERM-PLASM AS THE 



mitted, as E. Roth appears to believe. For instance, I freely admit 

 that the predisposition to an ' Exercierknochen ' varies, and that a 

 strongly marked 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 develope an ' Exercierknochen ' 

 without having- drilled, or that, after having- drilled, he could develope 

 it more easily than his father, on account of the drilling- throug-h 

 which the latter first acquired it. I believe that this is as im- 

 possible as that the leaf of an oak should produce a g-all, without 

 having- been pierced by a gall-producing insect, as a result of the 

 thousands of antecedent generations 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 unchangeable 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 conceiv- 

 able that organisms may exert a modifying influence upon their 

 germ-cells, and even that such a process is to a certain extent in- 

 evitable. The nutrition and growth of the individual must exercise 

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

 fluence 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 mole- 

 cular structure of the germ -plasm as would augment the predis- 

 position 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 

 reaction 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 knowledge there is reason for doubting whether 

 such reaction can occur at all ; but, if it can take place, ai; 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 influenced by the latter. In 

 the case of the 'Exercierknochen' there would be practically no 

 change in the general nutrition, but if such a bony growth could 



