338 CLASSICS OF MODERN SCIENCE 

 sion of acquired characters — up to that time generally accepted — is, to 

 say the least, very far from being proved, and that entire classes of 

 facts which have been interpreted under this hypothesis may be quite 

 as well interpreted otherwise, while in many cases they must be ex- 

 plained differently. I have shown that there is no ascertained fact 

 which, at least up to the present time, remains in irrevocable conflict 

 with the hypothesis of the continuity of the germ-plasm ; and I do not 

 know any reason why I should modify this opinion to-day, for I have 

 not heard of any objection which appears to be feasible. E. Roth has 

 objected that in pathology we everywhere meet with the fact that ac- 

 quired local disease may be transmitted to the offspring as a predis- 

 position; but all such cases are exposed to the serious criticism tUat 

 the very point that first needs to be placed on a secure footing is in- 

 capable of proof, viz., the hypothesis that the causes which in each 

 particular case led to the predisposition were really acquired. It is 

 not my intention, on the present occasion, to enter fully into the ques- 

 tion of acquired characters ; I hope to be able to consider the subject 

 in greater detail at a future date. But in the meantime I should wish 

 to point out that we ought, above all, to be clear as to what we really 

 mean by the expression ''acquired character." An organism cannot 

 acquire anything unless it already possesses the predisposition to ac- 

 quire it : acquired characters are therefore no more than local or some- 

 times general variations which arise under the stimulus provided by 

 certain external influences. If by the long-continued handling of a 

 rifle, the so-called '' Exercierknochen" (a bony growth caused by the 

 pressure of the weapon in drilling) is developed, such a result depends 

 upon the fact that the bone in question, like every other bone, contains 

 within itself a predisposition to react upon certain mechanical stimuH, 

 by growth in a certain direction and to a certain extent. The predis- 

 position towards an ''Exercierknochen" is therefore already present, 

 or else the growth could not be formed; and the same reasoning 

 applies to all other ''acquired characters." 



Nothing can arise in an organism unless the predisposition to it is 

 pre-existent, for every acquired character is simply the reaction of the 

 organism upon a certain stimulus. Hence I should never have 

 thought of asserting that predispositions cannot be transmitted, as E. 

 Roth appears to believe. For instance, I freely admit that the predis- 

 position to an '' Exercierknochen" varies, and that a strongly marked 



