ALBUMINOUS SUBSTANCES OR PROTEIDS. 345 



somewhat the albuminoids in their properties. Their charac- 

 teristic feature is the power of effecting changes in other or- 

 ganic substances, but the true cause of this action is unknown. 

 The most important cryptolites are pepsin, ptyalin, and pan- 

 creatin. 



Pepsin is the active principle of gastric juice, capable of con- 

 verting albumin readily into soluble peptones. Saccharated 

 pepsin, Pepsinum saccharatum, is officinal. Pepsin, obtained from 

 the mucous membrane of the stomach of the hog, is mixed with 

 powdered sugar of milk; this mixture is a white powder, not 

 completely soluble in water, but readily and completely dis- 

 solves on the addition of a small quantity of hydrochloric acid. 

 One part of saccharated pepsin dissolved in 500 parts of water, 

 acidulated with 7.5 parts of hydrochloric acid, should dissolve 

 at least 50 parts of hard-boiled egg-albumin, in 5 or 6 hours, at 

 a temperature of 38-40. 



Ptyalin is a compound found in saliva, and having the prop- 

 erty of converting starch into dextrine. 



Pancreatin, the active principle or principles of the pancreatic 

 secretion, is capable of converting starch into sugar, albumins 

 into peptones, neutral fats into emulsions, and also into glycerine 

 and fatty acids. 



Gelatinoids. To this group belongs a number of substances 

 occurring in bones, skins, horns, hair, nails, feathers, etc., and 

 having generally the property of forming a jelly with water. 

 The organic matter in bones, usually called ossein, contains, be- 

 sides an albuminous substance, the two gelatiuoids collagen and 

 gelatin, an impure mixture of which forms common glue. 



QUESTIONS. 



481. To which class of substances is the term proteids applied, and 

 which elements enter into their composition ? 



482. By what processes are albuminous substances formed in nature, 

 and where do they occur ? 



483. State the general properties of albuminous .substances. 



484. How are proteids acted upon by heat, nitric acid, and Millon's 

 reagent ? 



485. Into which three groups may proteids be classified, and how do 

 they differ from each other? 



