THE CAUSATION OF DISEASE. 21 5 



ticular E, and the instability of the E is sufficiently evidenced 

 by the fact that successive generations of individual families 

 follow in a large degree different callings. Wherefore we can, 

 11 priori, conclude that civilized people exhibit variations greatly 

 in excess of primitive tribes, and the greater the number of 

 natural variations the greater the room for unfavourable varia- 

 tions, and therefore for disease. The converse is also true : the 

 greater the number of natural variations, the greater is the 

 room for favourable variations. Hence it is that prodigies — 

 i.e., individuals, who in some respect, or respects, stand head 

 and shoulders above their fellows — are probably more common 

 in civilized communities. 



Similarly, we may be equally sure that owing to the com- 

 parative simplicity and stability of the E, variations are less 

 numerous among simple agricultural communities than among 

 the inhabitants of towns. 



A further cause of increase in the number of variations 

 occurring in civilized communities is the commingling and 

 intermarriage of different races ; for crossing is a recognized 

 cause of variations. 



Variations, then, being so abundant among civilized peoples, 

 we may be sure that natural selection will be active. 



In our study of this subject from the pathological point of 

 view, it will be convenient to arrange the variations under four 

 heads. Man maybe regarded as a two-sided organism — (1) as 

 a thinking being, (2) as merely corporeal — and he may vary 

 in one or other of these respects. Thus we have two great 

 classes of variations — (1) mental variations and (2) bodily 

 variations. Although it is convenient thus to make a distinc- 

 tion between the mental and physical sides of man, the dis- 

 tinction is more or less artificial, owing to the close inter- 

 dependence of the two. Mind is in some way connected with 

 matter, more particularly with nervous matter : it is depen- 

 dent upon the nervous organization of the cortex, and all 

 mental variations are in reality structural variations of a certain 

 portion of the nervous system. 



Setting aside this objection, however, the division into 

 mental and bodily variations admits of a further subdivision, 

 and one especially important from the medical point of view — 



Q 2 



