i8o MENDELISM CHAP. 



at present very little definite evidence for supposing that 

 what appear to be special forms of ability may be due to 

 specific factors. Hurst, indeed, has brought forward 

 some facts which suggest that musical sense sometimes be- 

 haves as a recessive character, and it is likely that the 

 study of some clean-cut faculty such as the mathematical 

 one would yield interesting results. 



The analysis of mental characters will no doubt be 

 very difficult, and possibly the best line of attack is to 

 search for cases where they are associated with some 

 physical feature such as pigmentation. If an association 

 of this kind be found, and the pigmentation factors be 

 determined, it is evident that we should thereby obtain 

 an insight into the nature of the units upon which mental 

 conditions depend. Nor must it be forgotten that men- 

 tal qualities, such as quickness, generosity, instability, 

 etc., qualities which we are accustomed to regard as 

 convenient units in classifying the different minds with 

 which we are daily brought into contact, are not 

 necessarily qualities that correspond to heritable units. 

 Effective mental ability is largely a matter of tempera- 

 ment, and this in turn is quite possibly dependent upon 

 the various secretions produced by the different tissues 

 of the body. Similar nervous systems associated with 

 different livers might conceivably result in individuals 

 upon whose mental ability the world would pass a very 

 different judgment. Indeed, it is not at all impossible 



