i86 Journal of Comparative Neurology. 



strength and shrink; and just so the brain needs exercise, and 

 in fact, earnest, hard lal)or, but not too one-sided, in order to 

 become and remain strong and healthy. Over-weariness and 

 over- exertion, however, injure the brain as they injure muscles 

 and nerves. To furnish power and working capacity, the mus- 

 cles and nerves require a sufficient amount of such nourishment 

 as will produce matter and force ; but over-feeding is an injury. 

 It is just so with the brain. 



Sleep is the indispensable rest of the brain during which it 

 recovers the substance lost by the wear of the day and gathers 

 up strength. Good sleep is the fundamental requirement for 

 brain health. Every nerve stimulant, and on the other hand all 

 substances that produce artificial sleep, are nerve poisons and 

 are to be condemned by a healthy nerve hygi^-ne. The worst- 

 foes of the human brain are alcohol, morphia, ether, cocaine, 

 and the like. Their use is never justified except very temporar- 

 ily as medicine, or in order to allay the pain and the agony of 

 death in a fatal illness. 



Every one who desires to secure and to stren.^then a healthy 

 and useful brain, must really lal)ar, and that daily, and not too 

 little. Four hours of work a day for a healthy being is alto- 

 gether too little. Let any one spend his time in enjoyment and 

 idleness, and enjoyment soon ceases to be enjoyment. He will 

 accumulate artificial wants in ever increasing number- until 

 they burden his life. He will become more and more depend 

 ent and morose. His mental horizon will grow narrower con 

 tinually and more rigid. The plastic brani of youth, that is, its 

 docility and adaptability, will become less and less active and 

 capable of comprehending and elaborating new thoughts. 



On the other hand, mental labor preserves the plasticity of 

 the brain to a much more advanced age. Idlers, therefore, in 

 spite of the best brain capacity, become prematurely old men- 

 tally, narrow-hearted, limited in horizon, and not seldom abso- 

 lutely stupid. We often observe moderately gifted students be 

 coming, by means of work, men of power, and highly gifted 

 young men, as a result of idleness, gradually grow useless, 

 peevish, and now and then nariow-minded Philistine-. 



Secondly, one must not overwork. The work day must 



