536 APPLIED BIOLOGY 



duce the necessary strain to the minimum and to follow it 

 with as much recreation as possible. 



The importance of fads and avocations as a means to mental 

 and physical recreation is great. Every man and woman 

 should cultivate at least one hobby. Even collecting postage- 

 stamps, coins, and natural-history specimens may be made an 

 important daily relief to a nervous system tired by the reg- 

 ular day's work ; but best of all avocations are those which 

 are as far different as possible from the regular work, e.g., a 

 greenhouse, a garden, or a work-shop for a man engaged in 

 mental work. 



But overwork is not all due to excessive exercise of the 

 nervous organs directly, for physical work may lead to ner- 

 vous disturbance. This is obviously due to the fact that mus- 

 cular contraction occurs only as the result of nervous action. 

 Moreover, there may be the added effect of the wearisome 

 monotony of uninteresting toil. 



The close relation of muscular and nervous work points 

 to the important hygienic law that mental work should not 

 be forced after physical exhaustion, or physical work after 

 becoming mentally tired. The time for hard physical exercise 

 is not near the close of a day of such intense mental strain 

 that the tired nervous system seems to rebel at lashing the 

 muscles into action. That is certainly a time to rest or rec- 

 reate in any way which is not approached as an unpleasant 

 duty. Conversely, the time for hard study is not at the close 

 of a day of exhausting physical work. Whether mental work 

 may safely succeed physical activity, or vice versa, usually 

 depends upon whether one finds it possible to take up the 

 change of work without constantly goading oneself against 

 a feeling of exhaustion. Ambitious workers will not meet 

 with the one great danger in this advice; namely, that of 

 confusing real exhaustion and mere laziness. 



460. Sleep. Probably more important than any other 

 rules of hygiene are those concerning sleep. Loss of sleep 



