1 6 CHEMICAL COMPOSITION OF HUMAX BODY. 



from the surface of mucous membrane, and floating in a 

 peculiar clear and viscid fluid. But under the name of 

 mucus, several various substances are included of which 

 some are morbid albuminous secretions containing mucus 

 and pus-corpuscles, and others consist of the fluid secretion 

 variously altered, concentrated, or diluted. Mucus contains 

 an albuminous substance, termed mucin. It differs from 

 albumen chiefly in not containing sulphur. 



Pepsin and other albuminous fermen ts, as they are some- 

 times called, will be described in connection with the secre- 

 tions of which they are the active principles. And the 

 various colouring matters, as of the blood, bile, &c., will be 

 also considered with the fluids or tissues to which they 

 belong. 



Besides the above-mentioned organic nitrogenous com- 

 pounds, other substances are formed in the living body, 

 chiefly by decomposition of nitrogenous materials of the 

 food and of the tissues, which must be reckoned rather as 

 temporary constituents than essential component parts of 

 the body ; although from the continual change, which is a 

 necessary condition of life, they are always to be found in 

 greater or less amount. Examples of these are urea, uric, 

 and hippuric acid, creatin, creatinin, leucin, and many 

 others. 



Such are the chief organic substances of which the 

 human body is composed. It must not be supposed, how- 

 ever, that they exist naturally in a state approaching that 

 of chemical purity. All the fluids and tissues of the body 

 appear to consist, chemically speaking, of mixtures of 

 several of these principles, together with saline matters. 

 Thus, for example, a piece of muscular flesh would yield 

 fibrin, albumen, gelatin, fatty matters, salts of soda, 

 potash, lime, magnesia, iron, and other substances, such as 

 creatin, which appear passing from the organic towards 

 the inorganic state. This mixture of substances may be 

 explained in some measure by the existence of many 



