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 with the same 

 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 wastes. 

 We thus perceive that different organs of our Bodies have 

 yery different endowments and serve for very distinct pur- 

 poses; and here again the study of infernal organs shows 

 us that the varieties of quality observed on the exterior are 

 but slight indications of differences of property which per- 

 vade 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 composing the bones and teeth; others, as 

 the muscles, are soft and capable of changing their form; 

 and still others are capable of working chemical changes 

 by which such peculiar fluids as the bile or the saliva are 

 produced. We find elsewhere a number of tissues -'com- 

 bined to form a tube adapted to receive food and carry it 

 through the Body for digestion, and again similar tissues 



