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 being 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 endowments and serve 

 for very distinct purposes; and here also the study of internal 

 organs shows us that the varieties of quality observed on the ex- 

 terior are but slight indications of differences of property which 

 pervade the whole, being sometimes dependent on the specific 

 characters of the tissues concerned 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 com- 

 posing 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 dif- 

 ferently arranged to receive the air which we breathe. in, and ex- 

 pel 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 the Body offers clearly even a more 

 complex subject of study than its structure. 



Physiological Properties. In common with inanimate objects 



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