GELATINOUS SUBSTANCES. n 



The oily or fatty matter which, enclosed in minute cells, 

 forms the essential part of the adipose or fatty tissue of the 

 human body (p. 38), and which is mingled in minute par- 

 ticles in many other tissues and fluids, consists of a mixture 

 of stearin, palmitin, and olein. The mixture forms a clear 

 yellow oil, of which different specimens congeal at from 

 45 to 35. 



Cholesterin, a fatty matter which melts at 293 F., and is 

 therefore, alwaj's solid at the natural temperature of the 

 body, may be obtained in small quantity from blood, bile, 

 and nervous matter. It occurs abundantly in many biliary 

 calculi ; the pure white crystalline specimens of these con- 

 cretions being formed of it almost exclusively. Minute 

 rhomboidal scale-like crystals of it are also often found 

 in morbid secretions, as in cysts, the puriform matter of 

 softening and ulcerating tumours, &c. It is soluble in 

 ether and boiling alcohol; but alkalies do not change 

 it ; it is one of those - fatty substances which are not 

 saponifiable. 



The azotized or nitrogenous principles in the human body 

 include what may be called the proper gelatinous and albu- 

 minous substances, besides others of less definite rank and 

 composition, as pepsin and ptyalin, horny matter or keratin, 

 many colouring and extractive matters, &c. 



The gelatinous substances are contained in several of the 

 tissues, especially those which serve a passive mechanical 

 office in the economy ; as the cellular, or fibro-cellular 

 tissue in all parts of the body, the tendons, ligaments, 

 and other fibrous tissues, the cartilages and bones, the 

 skin and serous membranes. These, when boiled in 

 water, yield a material, the solution of which remains 

 liquid while it is hot, but becomes solid and jelly-like on 

 cooling. 



Two varieties of these substances are described, gelatin 

 and chondrin, the latter being derived from cartilages, 

 the former from all the other tissues enumerated above, 



