102 PHYSIOLOGY. 



dead man has the same organization as when alive. It 

 is, therefore, far better to confess our ignorance, and say 

 with John Hunter, " life is a property we do not under- 

 stand." 



33. All the actions or functions of the body are mutually 

 dependent on each other. They constitute a circle, with- 

 out beginning or end. The motion of the blood depends on 

 the action of the heart and arteries ; the action of the heart 

 and arteries depends on the presence of blood. The heart 

 cannot act without the action of the lungs ; the lungs can- 

 not act without the action of the heart. Neither lungs nor 

 heart can act without the influence of the brain ; the brain 

 would have no influence, were it not for the action of the 

 lungs and heart. 



34.^ Thus the steam of a steam-engine works a bellows 

 which blows a fire that produces the steam J It would be as 

 difficult in this case, as in that of the animal functions to 

 say, which of these might be easiest dispensed with. If we 

 spare the bellows, the fire will not burn ; if we spare the fire, 

 the steam will not be raised ; if we spare the steam, the bel- 

 lows will not be worked ; so that if we spare either fire, bel- 

 lows, or steam, the machinery must stop* So it is in the 

 human body. 



35. The functions which fall within the scope of this 

 work to notice, may be divided into three classes ; l( vital ; 

 2, nutritive ; and 3, sensorial. ) {The vital functions are those 

 which are every moment essential to preserve lifejfc They 

 also may be considered as three in number, viz : innerva- 

 tion, circulation, and respiration ; or the functions of the 

 nervous system, those of the heart, and those of the lungs. 



36. fThe nutritive functions preside over the growth and 

 nutrition of the body* By their influence, the food is as- 

 similated, and becomes a part of our structures ; while all 

 the waste materials and worn-out elements are expelled from 

 the system. It thus embraces four functions ; digestion, 

 absorption, nutrition, and secretion. 



