22 TEXT-BOOK OF PHYSIOLOGY. 



eyes, skin and hair. The amount of iron contained in a body weighing 70 

 kilograms is about 2.2 gm. It exists under various forms e.g., ferric oxid, 

 and in combination with organic compounds. 



Chemic analysis thus shows that the chemic elements into which the 

 compounds may be resolved by an ultimate analysis do not exist in the 

 body in a free state, but only in combination, and in characteristic pro- 

 portions, to form compounds whose properties are the resultant of those of 

 the elements. Of the four principal elements which make up 97 per cent, 

 of the body, O, H, N are extremely mobile, elastic, and possessed of great 

 atomic heat. C, H, N are distinguished for the narrow range of their 

 affinities, and for their chemic inertia. C possesses the greatest atomic 

 cohesion. O is noted for the number and intensity of its combinations. 



As the properties of the compounds formed by the union of elements 

 must be the resultants of the properties of the elements themselves, it follows 

 that the ternary compounds, starches, sugars, and fats must possess more 

 or less inertia, and at the same time instability; while in the more complex 

 proteids, in which sulphur and phosphorus are frequently combined with 

 the four principal elements, molecular instability attains its maximum. 

 As all the foregoing compounds possess in varying degrees the properties of 

 inertia and instability, it follows that living matter must possess correspond- 

 ing properties, and the capability of undergoing unceasingly a series of 

 chemic changes, both of composition and decomposition, in response to the 

 chemic and physical influences by which it is surrounded, and which underlie 

 all the phenomena of life. 



PRINCIPLES OF DISSIMILATION. 



In addition to the previously mentioned compounds viz., carbo- 

 hydrates, fats, proteids, and inorganic salts there is obtained by chemic 

 analysis from the tissues and fluids of the body: 



1. A number of organic acids, such as acetic, lactic, oxalic, butyric, pro- 

 pionic, etc., in combination with alkaline and earthy bases. 



2. Organic compounds, such as alcohol, glycerin, cholesterin. 



3. Pigments, such as those found in bile and urine. 



4. Crystallizable nitrogenized bodies, such as urea, uric acid, xanthin, 

 hippuric acid, creatin, creatinin, etc. 



While some few of these compounds may possibly be regarded as neces- 

 sary to the physiologic integrity of the tissues and fluids, the majority of 

 them are to be regarded as products of dissimilation of the tissues and foods 

 in consequence of functional activity, and represent stages in their reduction 

 to simpler forms previous to being eliminated from the body. 



