SECTION I. 

 NUTRITION. 



CHAPTEE I. 



PROXIMATE PRINCIPLES IN GENERAL. 



THE study of NUTRITION begins naturally with that of the proximate 

 principles, or the substances entering into the composition of the dif- 

 ferent parts of the body, and the different kinds of food. In examining 

 the body, the anatomist finds that it is composed, first, of various parts, 

 which are easily recognized by the eye, and which occupy distinct situa- 

 tions. In the case of the human body, for example, a division is easily 

 made of the entire frame into the head, neck, trunk, and extremities. 

 Each of these regions, again, is found, on examination, to contain several 

 distinct parts, or "organs," which require to be separated from each 

 other by dissection, and which are distinguished by their form, color, 

 texture, and consistency. In a single limb, for example, every bone and 

 every muscle constitutes a distinct organ. In the trunk, we have the 

 heart, the lungs, the liver, spleen, kidneys, spinal cord, etc., each of 

 which is also a distinct organ. When a number of organs, differing in 

 size and form, but similar in texture, are found scattered throughout 

 the entire frame, or a large portion of it, they form a connected set or 

 order of parts, which is called a " system." Thus, all the muscles taken 

 together constitute' the muscular system ; all the bones, the osseous 

 system ; all the arteries, the arterial system. Several entirely different 

 organs may also be connected with each other, so that their associated 

 actions tend to accomplish a single object, and they then form an 

 " apparatus." Thus the heart, arteries, capillaries, and veins, together, 

 form the circulatory apparatus ; the stomach, liver, pancreas, intestines, 

 etc., the digestive apparatus. Every organ, again, on microscopic ex- 

 amination, is seen to be made up of minute bodies, of definite size and 

 figure, which are so small as to be invisible to the naked eye, and which, 

 after separation from each other, cannot be further subdivided without 

 destroying their organization. They are, therefore, called " anatomical 

 elements." Thus, in the liver, there are hepatic cells, capillary blood- 

 vessels, the fibres of Glisson's capsule, and the ultimate filaments of the 



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