PHYSIOLOGY OF THE CELL. 25 



in a free state, but only in combination, and in characteristic proportions, 

 to form compounds whose properties are the resultant of those of the elements. 

 Of the four principal elements which make up ninety-seven 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 great 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 proteins, 

 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 corresponding 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., carbohydrates, 

 fats, proteins, 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, propionic, 

 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. 



PHYSIOLOGY OF THE CELL. 



A histologic analysis of the tissues shows that they can be resolved into 

 simpler elements, termed cells, which may, therefore, be regarded as the 

 primary units of structure. Though cells vary considerably in shape, size, 



