24 CHEMICAL COMPOSITION OF HUMAN BODY. 



Horny Matter. The substance of the horny tissues, includ- 

 ing the hair and nails (with whalebone, hoofs, and horns), 

 consists of an albuminous substance, with larger proportions 

 of sulphur than albumen and fibrin contain. Hair contains 

 10 per cent, and nails 6 to 8 per cent, of sulphur. 



The horny substances, to which Simon applied the name of 

 keratin, are insoluble in water, alcohol, or ether; soluble in 

 caustic alkalies, and sulphuric, nitric, and hydrochloric acids; 

 and not precipitable from the solution in acids by ferrocyanide 

 of potassium. 



Mucus, in some of its forms, is related to these horny sub- 

 stances, consisting, in great part, of epithelium detached 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, con- 

 centrated, or diluted. Mucus contains an albuminous sub- 

 stance, termed mucin. It differs from albumen chiefly in not 

 containing sulphur. 



Pepsin and other albuminous ferments, as they are sometimes 

 called, will be described in connection with the secretions of 

 which they are the active principles. And the various color- 

 ing 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 compounds, 

 other substances are formed in the living body, chiefly by de- 

 composition of nitrogenous materials of the food and of the 

 tissues, which must be reckoned rather as temporary constitu- 

 ents 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 acids, creatin, 

 creatinin, leucin, and many others. 



Such are the chief organic substances of which the human 

 body is composed. It must not be supposed, however, that 

 they exist naturally in a state approaching that of chemical 

 purity. All the fluids and tissues of the body appear to con- 

 sist, chemically speaking, of mixtures of several of these prin- 

 ciples, 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 sub- 

 stances may be explained in some measure by the existence of 

 many different structures or tissues in the muscles ; the gelatin 



