FOUNDATION OF A THEORY OF HEREDITY. 169 



hypothesis of the transmission 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 explained 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 J has objected 

 that in pathology we everywhere meet with the fact that acquired 

 local disease may be transmitted to the offspring as a predispo- 

 sition ; but all such cases are exposed to the serious criticism that 

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

 incapable 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 question 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 ' ac- 

 quired character.' An organism cannot acquire anything unless it 

 already possesses the predisposition to acquire it : acquired cha- 

 racters are therefore no more than local or sometimes general 

 variations which arise under the stimulus provided by certain ex- 

 ternal influences. If by the long-continued handling of a rifle, the 

 so-called ' Exercierknochen ' (a bony growth caused by the pres- 

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

 upon the fact that the bone in question, like every other bone, con- 

 tains within itself a predisposition to react upon certain mechanical 

 stimuli, by growth in a certain direction and to a certain extent. 

 The predisposition 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 trans- 



1 E. Both, 'Die Thatsachen der Vererbung.' 2. Aufl., Berlin, 1885, p. 14. 



