EXERCISE IS RESTORED BY SLEEP. 943 



and his expenses 1000 pounds, it is obvious, that 

 unless the latter be materially diminished for a 

 time, his whole capital must be very soon ex- 

 hausted. In like manner, if the substance and 

 vital heat of the body be expended by exercise 

 of the brain, nerves, and voluntary muscles, with 

 twice the rapidity that they are replaced by re- 

 spiration and nutrition, it becomes evidently ne- 

 cessary that the activity of the system should be 

 suspended, until the loss is repaired, which is 

 most effectually accomplished during repose, 

 when the expenditure is at the minimum. Thus 

 it is, that although respiration is diminished 20 

 per cent, about the middle of night, even when 

 awake, if the body be at rest, according to the 

 experiments of Dr. Prout, and probably still 

 more during sleep ; yet the income greatly ex- 

 ceeds the waste. 



That a larger amount of animal heat is retained 

 in the body during sleep, when sufficiently 

 covered, than during the exercise of the day, 

 would appear from the fact, that the temperature 

 under the tongue is one or two degrees higher on 

 first awaking in the morning, than at bed time ; 

 except after exercise, or taking a hearty supper, 

 both of which augment respiration. This ex- 

 plains why it is that in hot countries, where 

 the inhabitants take an afternoon nap, the face, 

 neck, and whole surface of the boy, perspire 

 more than if awake at the same time, ceteris 

 paribus. And Sanctorius informs us, that during 



