EXTRACTIVE MATTERS. 25 



drochloric acids ; and not precipitable from the solution in 

 acids by ferrocyanide of potassium. 



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

 substances, 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, concentrated, or diluted. The true 

 chemical characters of this fluid are as yet incompletely 

 known. 



Extractive Matters. Under this name are included sub- 

 stances of mixed and uncertain composition, which form 

 the residue of animal matter when, from almost any of the 

 fluids or solids of the body, the albuminous, gelatinous, 

 and fatty principles have been removed. The remaining 

 animal matter is mixed with various salts, such as lactates, 

 chlorides, and phosphates, and is divisible into two princi- 

 pal portions, of which one is soluble in water alone, the 

 other in alcohol. 



Doubtless there are in these substances many distinct 

 compounds, of which some exist ready-formed in the body, 

 and some are formed in the changes to which the previous 

 chemical examinations have given rise. Many of them, 

 including kreatin and kreatinin, two principles originally 

 discovered among the extractive matters of muscular 

 tissue, but since found in the blood, urine, and elsewhere, 

 are no doubt products of the chemical changes that take 

 place in the natural waste and degeneration of the tissues, 

 and are substances that are to be separated from the 

 tissues for excretion. 



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 



