172 THE INDUCTIONS OF BIOLOGY 



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 heating, 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 ever kept in a state of integ- 

 rity by a repair which keeps pace with waste, or which 

 alternately falls behind and gets in advance of it to a very 

 sliglit extent. 



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

 see, that repair is most rapid when activity is most reduced. 

 Assuming that the organs which absorb and circulate nutri- 

 ment are in proper order, the restoration of the organism 

 to a state of integrity, after the disintegration consequent 

 on expenditure of force, is proportionate to the diminution 

 in expenditure of force. 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 that 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- 

 newal less than that which would have followed the greater 

 inactivity of slumber. We know, too, that when exhausted 

 by labour, sitting brings a partial return of vigour. And 

 we also know that after the violent exertion of runnini' 



