80 CREATIVE EVOLUTION [chap. 



the son, may have grown on the way by the effect of the 

 primitive impetus, and thus assured to the son a greater 

 suppleness than the father had, without troubling, so to 

 speak, about what the father did. So of many examples 

 drawn from the progressive domestication of animals: 

 it is hard to say whether it is the acquired habit that is 

 transmitted or only a certain natural tendency — that, 

 indeed, which has caused such and such a particular 

 species or certain of its representatives to be specially 

 chosen for domestication. The truth is, when every 

 doubtful case, every fact open to more than one inter- 

 pretation, has been eliminated, there remains hardly a 

 single unquestionable example of acquired and trans- 

 mitted peculiarities, beyond the famous experiments 

 of Brown-Sequard, repeated and confirmed by other 

 physiologists. 1 By cutting the spinal cord or the sciatic 

 nerve of guinea-pigs, Brown-Sequard brought about an 

 epileptic state which was transmitted to the descendants. 

 Lesions of the same sciatic nerve, of the restiform body, etc., 

 provoked various troubles in the guinea-pig which its 

 progeny inherited sometimes in a quite different form: 

 exophthalmia, loss of toes, etc. But it is not demonstrated 

 that in these different cases of hereditary transmission 

 there had been a real influence of the soma of the animal 

 on its germ-plasm. Weismann at once objected that the 

 operations of Brown-Sequard might have introduced cer- 

 tain special microbes into the body of the guinea-pig, 

 which had found their means of nutrition in the nervous 

 tissues and transmitted the malady by penetrating into 

 the sexual elements.' This objection has been answered 



1 Brown-Sequard, ' ' Nouvelles recherches sur Pepilepsie due a certaines 

 lesions de la moelle £pinieere et des nert's rachidiens" (Arch.de physi- 

 ologie, vol. ii., 1866, pp. 211, 422, and 497). 



2 Weismann, Aufsdtze uber Vererbung, Jena, 1892, pp. 376-378, and 

 also Vortrage uber Descendenztheorie, Jena, 1902, vol. ii., p. 76. 



