HUMAN PHYSIOLOGY. 



INTRODUCTION. 



I. PHYSIOLOGY is the study of the phenomena presented by 

 organized bodies, animal and vegetable. 



These phenomena are different from those presented by inorganic 

 substances. They require, for their production, the existence of 

 peculiarly formed animal and vegetable organisms, as well as the 

 presence of various external conditions, such as warmth, light, air, 

 moisture, &c. 



They are accordingly more complicated than the phenomena of 

 the inorganic world, and require for their study, not only a pre- 

 vious acquaintance with the laws of chemistry and physics, but, in 

 addition, a careful examination of other characters which are pecu- 

 liar to them. 



These peculiar phenomena, by which we so readily distinguish 

 living organisms from inanimate substances, are called Vital pheno- 

 mena, or the phenomena of Life. Physiology consequently includes 

 the study of all these phenomena, in whatever order or species of 

 organized body they may originate. 



We find, however^ upon examination, that there are certain 

 general characters by which the vital phenomena of vegetables 

 resemble each other, and by which they are distinguished from the 

 vital phenomena of animals. Thus, vegetables absorb carbonic 

 acid, and exhale oxygen ; animals absorb oxygen, and exhale car- 

 bonic acid. Yegetables nourish themselves by the absorption of 

 unorganized liquids and gases, as water, ammonia, saline solutions, 

 &c. ; animals require for their support animal or vegetable sub- 

 stances as food, such as meat, fruits, milk, &c. Physiologv, then, 

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