62 THE LAW OF BIRTHS AND DEATHS 



movement, but usually necessitate considerable muscular 

 exertion. The result is that the former is, as a rule, 

 a man of less bulk but of greater nervous energy, the 

 latter usually developing into a heavy, slow-moving, 

 slow-thinking individual, conspicuously deficient in nervous 

 energy. But this result could hardly be produced unless 

 the nervous system and nervous energy developed with 

 exercise. The greater quickness of movement which 

 marks the town-bred man as compared with the country- 

 bred man is obviously due to a greater expenditure of 

 nervous energy, and this can only result from an increase 

 of efficiency or of bulk, or both, on the part of the motor 

 centres or the motor nerves, or both. Seeing, also, that 

 the amount of energy developed is powerfully affected 

 both by the nature of the food and the climate, it would 

 be strange if exercise were the one factor by which it 

 is not affected. 



But there is a limit to the capacity of the organism 

 for producing energy, and this is fixed by its inherent 

 potentialities. Lagrange points out that exhaustion 

 will result from work which is beyond a man's strength, 

 even if he is well. He can perform such work only by 

 " taking from his nerves " that which his muscles are 

 unable to give. " The excessive exertion of the will in 

 work leads to nervous exhaustion. It is thus that we 

 eee horses rapidly waste and get ill, if they are forced 

 to draw too heavy a load, and their ardent and generous 

 nature impels them to go on working up to the last limit 

 of their strength." l 



Probably, most of the physical deficiencies shown by 

 the race in these days are the result of factory employ- 

 ment and similar occupations. Under the system of 

 division of labour it is commonly asserted that this or 



1 Physiology of Bodily Exercise, Fernand Lagrange, part iv, chap. iii. 





