216 THE INDUCTIONS OF BIOLOGY. 



until they ache or become stiff, and nerves of sense rendered 

 weary or obtuse by work, are organs so much wasted by action 

 as to be partially incompetent. 



Repair is everywhere and always making up for waste. 

 Though the two processes vary in their relative rates both 

 are constantly going on. Though during the active, waking 

 state of an animal waste is in excess of repair, yet repair is 

 in progress; and though during sleep repair is in excess of 

 waste, yet some waste is necessitated by the carrying on of 

 certain -never-ceasing functions. The organs of these never- 

 ceasing functions furnish, indeed, the most conclusive proofs 

 of the simultaneity of repair and waste. Day and night the 

 heart never stops beating, but only varies in the rapidity and 

 vigour of its beats ; and hence the loss of substance which its 

 contractions from moment to moment entail, must from 

 moment to moment be made good. Day and night the lungs 

 dilate and collapse; and the muscles which make them do 

 this must therefore be kept in a state of integrity by a repair 

 which keeps pace with waste, or which alternately falls behind 

 and gets in advance of it to a very slight extent. 



On a survey of the facts we see, as we might expect to see, 

 that the progress of repair is most rapid when activity is 

 most reduced. Assuming that the organs which absorb and 

 circulate nutriment are in proper order, the restoration of 

 the body to a state of integrity, after the disintegration con- 

 sequent on expenditure of energy, is proportionate to the 

 diminution in expenditure of energy. Thus we all know that 

 those who are in health, feel the greatest return of vigour 

 after profound sleep after complete cessation of motion. 

 We know that a night during which the quiescence, bodily 

 and mental, has been less decided, is usually not followed by 

 that spontaneous overflow of energy which indicates a high 

 state of efficiency throughout the organism. We know, 

 again, that long-continued recumbency, even with wakeful- 

 ness (providing the wakefulness is not the result of disorder), 

 is followed by a certain renewal of strength; though a re- 



