PROXIMATE PRINCIPLES. 27 



3. Organic Nitrogenized Substances. This class of prox- 

 imate principles is of organic origin, indefinite chemical com- 

 position, and non-crystallizable. Substances forming this 

 class are apparently the only principles which are endowed 

 with vital properties, taking materials for their regeneration 

 from the nutritive fluids, and appropriating them to form 

 part of their own substance. Considered from this point 

 of view, they are different from any thing which is met with 

 out of the living body. They are all, in the body, in a state 

 of continual change, wearing out and becoming effete, when 

 they are transformed into excrementitious substances, which 

 constitute the second grand division of proximate principles. 

 The process of repair in this instance is not the same as in 

 inorganic substances, which enter and are discharged from 

 the body without undergoing any- change. The analogous 

 substances which exist in food, undergo a very elaborate prep- 

 aration, by digestion, before they can even be absorbed by 

 the blood-vessels ; and still another change takes place 

 when they are appropriated by the various tissues. They 

 exist in all the solids, semi-solids, and fluids of the body, 

 never alone, but always combined with inorganic substances. 

 As a peculiarity of chemical constitution, they all contain 

 nitrogen, which has given them the name of Nitrogenized or 

 Azotized principles. As before intimated, they give to the 

 tissues and fluids their vital properties. In studying their 

 properties more fully, we shall see that they are by far the 

 most important elements in the organism. The elaborate 

 preparation which they require for absorption involves the 

 most important part of the function of digestion. Their ab- 

 solute integrity is necessary to the operation of the essential 

 functions of many tissues, as muscular contraction, or con- 

 duction of nervous force. An exact knowledge of all the 

 transformations which take place in their regeneration and the 

 process by which they are converted into effete or excremen- 

 titious matters, would enable us to comprehend nutrition, 

 which is the essence of physiology ; but as yet we know little 



