332 ACTION ON PROTEIDS. 



by concentrated solution of common salt. It is soluble in water in the 

 presence of weak acids and alkalies. It is precipitated by nitric acid 

 and adheres firmly to the walls of the reagent glass; it dissolves in 

 nitric acid with the aid of heat, giving an intense yellow colour, and is 

 again precipitated in the cold (E. Salkowski). The compound of 

 nitric acid with propeptone is of the nature of a salt, and it is 

 deposited in the form of sphseroids. 



By the continued action of the gastric juice, the propeptone passes 

 into a true soluble peptone. The unchanged albumin behaves like an 

 anhydride with respect to the peptone. The formation of peptone is 

 due to the taking up of a molecule of water, under the influence of the 

 Jiydrolytic ferment pepsin, and the action takes place most readily at the 

 temperature of the body. Gelatin is changed into a gelatin-peptone. 

 The greater the amount of pepsin (within certain limits), the more 

 rapidly does the solution take place. The pepsin suffers scarcely any 

 change, and if care be taken to renew the hydrochloric acid so as to 

 keep it at a uniform amount, the pepsin can dissolve new quantities of 

 albumin. Still, it seems that some pepsin is used up in the process of 

 digestion (Griitzner). Proteids are introduced into the stomach either 

 in a solid (coagulated) or fluid condition. Casein alone of the fluid 

 forms is precipitated or coagulated, and afterwards dissolved. The 

 non-coagulated proteids are transformed into syntonin, without being 

 previously coagulated, and are then changed into propeptone and 

 directly peptonised, i.e., actually dissolved. 



When albumin is digested by pepsin at the temperature of the body, 

 a not inconsiderable amount of heat disappears, as can be proved by 

 calorimetric experiment (Maly). Hence, the temperature of the chyme 

 in the stomach falls 0'2-0-6C in 2-3 hours (v. Vintschgau and 

 Dietl). 



Coagulated albumin may be regarded as the anhydride of the fluid 

 form, and the latter again as the anhydride of peptone. The peptones, 

 therefore, represent the highest degree .of hydration of the proteids. 



Hence, peptones may be formed from proteids by those reagents which usually 

 cause hydration, viz., treatment with strong acids, (from fibrin, with 0'2 HC1 

 v. Wittich), caustic alkalies, putrefactive, and various other ferments and ozone 

 (Gorup-Besanez). 



The anhydride proteid has been prepared from the hydrated form. 

 Henniger and Hofmeister, by boiling pure peptone with dehydrating 

 substances (anhydrous acetic acid at 80C.), have succeeded in decom- 

 posing it into a body resembling syntonin. 



Properties of Peptones: (1) They are completely soluble in water. 

 (2) They diffuse very easily through membranes (Funke), and are 

 twelve times as diffusible as fluid albumin ; the fibrin-peptone is said 



