CHAPTER II. 



THE FUNDAMENTAL PHYSIOLOGICAL ACTIONS. 



The Properties of the Living Body. When we turn 

 from the structure and composition of the living Body to 

 consider its powers and properties we meet again with great 

 variety and complexity, the most superficial examination be- 

 ing sufficient to show that its parts are endowed with very 

 different faculties. Light falling on the eye arouses in us a 

 sensation of sight, but falling on the skin has no such effect; 

 pinching the skin causes pain, but pinching a hair or a nail 

 does not; when the ears are stopped, sounds arouse in us no 

 sensation; we readily recognize, too, hard parts formed for 

 support, joints to admit of movements, apertures to receive 

 food and others to get rid of waste. We thus perceive that 

 different organs of our Bodies have very different endow- 

 ments and serve for very distinct purposes; and here also 

 the study of internal organs shows us that the varieties of 

 quality observed on the exterior are but slight indications of 

 differences of property which pervade the whole, being some- 

 times dependent on the specific characters of the tissues con- 

 cerned and sometimes upon the manner in which these are 

 combined to form various organs. Some tissues are solid, 

 rigid and of constant shape, as those composing the bones 

 and teeth; others, as the muscles, are soft and capable of 

 changing their forms; and still others are capable of working 

 chemical changes by which such peculiar fluids as the bile 

 and the saliva are produced. We find elsewhere a number of 

 tissues combined to form a tube adapted to receive food and 

 carry it through the Body for digestion, and again similar 

 tissues differently arranged to receive the air which we breathe- 

 in, and expel it after abstracting part of its oxygen and 

 adding to it certain other things; and in the heart and blood- 

 vessels we find almost the same tissues arranged to propel 

 and carry the blood over the whole Body. The working of 



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