HEREDITY OF ACQUIRED CHARACTERS CUENOT. 337 



case of the mutilations and the experiments of Brown-Sequard). In 

 truth the decisive experiment, verified and certain, is still lacking. 

 As for the nonexperimental proofs, they are always subject to discus- 

 sion and can never attain beyond second rank. 



As it is necessary, however, to hold some opinion on a question 

 so important that it dominates all the conceptions of evolution, we 

 must decide for ourselves according to the relative weight which we 

 attribute to the various arguments, and naturally each one of us 

 holds the more strongly to his own view, the more this view allows 

 for a greater degree of personal appreciation. Some, partisans of 

 heredity, receive with pleasure experiments or observations, even 

 mediocre, which seem to them to constitute proofs; others who re- 

 ject it, hunt for weak points in the demonstrations, and usually 

 find them. It is almost a matter of faith, of nationality. The great 

 majority of French zoologists favor the affirmative, following Gi- 

 ard, Edmond Perrier, Le Dantec, F. Houssay, Delage, all more 

 or less Lamarckists; the Americans, except some paleontologists, 

 are nearly all for the negative. I am perfect^ ready to admit that 

 up to the present I have put mj'self on the negative side. 



It is obvious that there are categories of acquired characters 

 arising from different causes: (1) Mutilations; (2) the effects of 

 parasitic diseases producing a general intoxication; (3) the action 

 of the great natural factors, light, temperature, humidity, salinity, 

 nourishment; (4) the effects of use or those of disuse; (5) the 

 psychic acquisitions of training, of instruction. In my opinion, the 

 negative demonstration, that of the nonheredity of acquired char- 

 acters of one of these categories, is of value for that one only, and 

 can not legitimately be extended to the others, for if there are cer- 

 tain acquisitions of the body which are not transmitted to the sexual 

 cells, the bearers of the hereditary patrimony, it does not neces- 

 sarily follow that the same is true for all. But, on the other hand, 

 if there were an experiment which showed indisputably the he- 

 redity of a truly acquired character, it would be a strong proba- 

 bility for some other categories, for although we do not understand 

 completely how an acquired bodily modification can add itself even 

 in weakened form to the hereditary patrimony, if the fact were 

 proved one single time, the argument of incomprehension would lose 

 all of its force. 



For the first category of acquired characters, it can be said that 

 the answer is definite; since the critiques and the experiments of 

 Weismann, many times repeated, no one believes any longer in the 

 heredity of mutilations. Every-day observations confirm those of 

 biologists and it is certain that the pseudo-examples of the trans- 

 mission of mutilations that are quite often reported among domestic 



