iv WEISMANN ON ACQUIRED CHARACTERS 175 



what causes ; we only know that at least a great proportion 

 of them proceed from the germ itself, and must therefore be 

 due to alteration of the germinal substance. 



" If Virchow could show that any single one of these 

 hereditary deformities had its origin in the action of some 

 external cause upon the already formed body (soma) of the 

 individual, and not upon the germ-cell, then the inheritance 

 of acquired characters would be proved. But this no one has 

 yet succeeded in proving, often as it has been maintained." 

 The inheritance of artificially produced diseases, accord- 

 ing to Weismann, is no proof. " Unless I am much 

 mistaken," he says, " the transmission of acquired epilepsy to 

 the following generation, the occurrence of which is not to be 

 denied, is not due to inheritance, but to infection of the germ, 

 to the transference of living disease-producing organisms." 



As Weismann himself in another place makes use of the 

 expression that his view is a matter of conviction, that no 

 proof of it can be brought forward, all that can be done is to 

 bring against it, as we have done, the facts that contradict it. 

 In particular, that view seems to me to have no prospect of 

 being accepted so long as there is no peculiar pathology of 

 the germ -plasm, and so long as the assumption that the 

 physiology of the germ-cells is so exceptional in comparison 

 with that of the other cells of the body, as Weismann's theory 

 requires, is unsupported by any basis of proof. 



Of course it is true that the consideration on account of 

 which he proposed his theory seems to be in Weismann's 

 favour, namely, that this theory would explain the portrait- 

 like inheritance of characters, and reversion. But it is a 

 question whether such an explanation is not possible on other 

 grounds. " We are well aware," he remarks in one of his 

 latest writings, 1 " that all bodily and mental peculiarities may 



1 Ueber den R&ckschritt der Natur, Berichte der naturforschenden Gesellschaft 

 zu Freiburg i. B. Bd. ii. Heft i. 1886. 



