88*2 EXPENDITURE OF CALORIC BY EXERCISE 



although it must be a'dmitted that imperfect 

 nourishment, impure air, and intemperance, aug- 

 ment the evil. The same observation applies to 

 coach horses, which are worn out in a few years 

 by active service. And it is said that in the hilly 

 parts of Scotland, the shepherd's dog cannot 

 labour above five or six years, but eight or nine 

 years on the low lands. 



The waste of the body is accelerated by intense 

 cold, for the same reason that it is augmented by 

 exercise ; that is, because the animal heat by 

 which the molecules of arterial blood are united 

 with the solids is abstracted by the surrounding 

 media more rapidly than it is obtained by respi- 

 ration ; so that notwithstanding the natives of 

 the polar regions consume a larger amount of 

 food than the inhabitants of warm and temperate 

 climates, they are stinted in growth, and life is of 

 short duration. The rapid expenditure of caloric 

 by exercise arid exposure to cold, creates the 

 , sensation of a vital want, which prompts the in- 

 dividual to take more deep and frequent inspi- 

 rations ; while the consequent waste of the solids 

 creates the sensation of hunger, which prompts 

 us to take more or less food, according to the 

 amount of waste. 



In like manner, the expenditure of animal heat 

 and of the solid tissues by exercise, faster than 

 they are renewed by respiration and nutrition, 

 diminishes the vital energy of the brain, nerves, 



