68 THE LAW OF BIRTHS AND DEATHS 



follows that a higher development of the nervous system 

 will, other things equal, lead to a higher development 

 of nervous energy ; but quantity is not of so much 

 importance as quality. Idiots sometimes have very large 

 brains. Then there is the fact that brains increase in 

 average size as we proceed northward a fact which 

 probably has something to do with the maintenance of 

 heat. Again, there is what Herbert Spencer once called 

 " a small brain in a state of intense activity." The 

 possessors of the higher forms of intellect are often excelled 

 in nervous energy by people of a lower intellectual order. 

 The cerebral system being developed by exercise, an 

 environment leading to incessant mental activity is 

 favourable to the development of nervous energy. Mental 

 activity does not necessarily mean study or any of the 

 higher forms of intellectual effort. The complex environ- 

 ment of a modern city leads to an enormous and almost 

 unsuspected amount of mental activity. The mind, 

 and more particularly the unconscious mind, is constantly 

 occupied in recording or acting upon myriads of sugges- 

 tions which beat upon it from all sides. It is evident 

 that the more complex the environment the greater 

 will be the multitude of suggestions and the greater the 

 multitude of cerebral reactions. Hence the larger brains, 

 the greater mental activity, and the higher development 

 of nervous energy in the average city man as compared 

 with the average country man. 



The amount of nervous energy produced is affected by 

 many subtle influences. Thus bad news usually has a 

 depressing effect, and tends to take the energy out of the 

 average individual. Sometimes, however, it stimulates to 

 feverish activity, as when news is received of a danger 

 which may be avoided by exertion. The subtlety of the 

 nervous force is seen in the ease with which a man of 



