io Heredity. 



which descend from them, provided the changes acquired are 

 common to the two sexes, or to those which have produced new 

 individuals.' * 



Still, these two opposite opinions, both of which may be sup- 

 ported by facts, can be reconciled if we bear in mind that there 

 are modifications which, by their very nature, are in antagonism 

 with everything around them, and for which, in consequence, the 

 conditions of existence grow more and more difficult ; just as there 

 are others which, when in conformity with everything around them, 

 may become permanent by either natural or artificial selection : 

 so that all things conspire to blot out the former class of modifi- 

 cations, and to perpetuate the latter. We shall meet this difficulty 

 again, when treating of psychological heredity, and will there 

 consider it more fully. 



We have now to speak of the last form of heredity that of 

 disease. This seems to have been observed from the foundation 

 of the art of medicine in all times, in every land, and in every 

 nation. Even the Greek physicians recognized hereditary diseases 

 (voaoi K\r)povo[UKai). And yet in modern times the heredity of 

 disease has given rise to all manner of debates among medical 

 men. It would be beyond our subject, and beyond our 

 power, to discuss this point It is enough to say that the 

 question appears to be substantially settled by the fact that the 

 sturdiest opponents of morbid heredity admit, if not the heredity 

 of disease itself, at least the heredity of a disposition to it. In 

 Dr. Lucas's work on Heredity will be found facts of all kinds, 

 sufficiently numerous and sufficiently clear to warrant a conclusion. 



This hasty physiological sketch will show that the law of 

 heredity influences every form of vital energy a fact which is 

 generally known and admitted. Is the same to be said with 

 regard to the psychological aspect of the question ? This we pro- 

 pose now to consider, and to begin with the study of the facts. 



1 In regard to the physiological side of this controversy, see the Bulletins 

 de la Societ^ d* Anthropologie, tome i. p. 339, and particularly p. 551, seq.j 

 tome ii,, De VHh'edite dcs Anomalies. 



