212 THE THEORIES OF EVOLUTION 



however, does not claim that all characters are trans- 

 missible; its exponents are satisfied if some characters 

 are proved to be transmissible. 



Strange as it may seen, diseases, non-congenital but 

 acquired, cannot furnish evidence for or against the 

 idea of transmission, for the cases cited admit of too 

 many different interpretations. 



Not only is it very difficult to determine whether a 

 disease is congenital or acquired, but in the case of 

 bacterial diseases the pathogenic microbe can be trans- 

 mitted directly in the germ, and this does not con- 

 stitute a case of hereditary transmission. Many dis- 

 eases whose causes are unknown may some day be 

 traced to a microbian infection. In other cases when 

 the appearance of the disease synchronises with the 

 production of a certain toxin or is determined by a 

 certain chemical phenomenon, the relevant substance 

 may pass directly from the organism of the parent 

 into that of the offspring. Sanson l cites the case of 

 a flock of sheep which, after staying in a damp loca- 

 tion, contracted an articular disease. Although the 

 flock was later transferred to a dry location, several 

 generations of the sheep suffered from that disease 

 until all the affected individuals were replaced by 

 other individuals of the same race which had not been 

 exposed to the same influences. This was a case of 



iSakson. L'HSriditS normale et pathologique (1893). 



