302 PHYSIOLOGY AND HEALTH. 



of the ship's labor, and perform a stout man's duty. He 

 must take his turn, and watch night as well as day. He can 

 never expect to have an entire night's rest. 



Making all due allowance for the difference of habits of 

 many in these several classes, admitting that the poor la- 

 borer is often an invalid, and is worse clothed and fed than 

 the farmer, and that more accidents happen to both the laborer 

 and the sailor than to the farmer, and even other circum- 

 stances that interfere with the full enjoyment of health, still 

 much of this great difference of longevity a measure of 

 years on earth given to the farmer about forty per cent, 

 greater than that given to the laborer and the sailor must 

 be charged to that excess of toil which wears out the man 

 prematurely. 



CHAPTER XV. 



Languor always succeeds great Efforts. Serious Injury may follow. 

 Growing Children need various and light Exercises. Youths 

 cannot endure the full Labor of mature Men. 



698. THE period of vigor and of a man's productive 

 power is shortened, the sum of the whole life's exertion is 

 materially diminished, and its last stages rendered compara- 

 tively useless, by attempting to work beyond the power of 

 permanent endurance. This is the result of long-continued 

 over-exertion. But even if it is not long continued, if it is 

 merely temporary, the same result of languor, and lessened 

 ability for labor, follows for a proportion ably short period. 

 An extraordinary labor of one day is followed by extraor- 

 dinary languor the next; and whether this greater exertion, 

 this excess of waste of the powers over the nutrition, be more 

 or less, it must be followed by a proportionate feebleness. 



099. Excessive temporary exertions are followed, not only 



