PEPTONE. 71 



coagulate, and become extremely insoluble and lose their former 

 characters. They are but very slightly acted on by weak acids, 

 even when warmed. Strong acids dissolve them, but this solution 

 is associated with a destructive change. They are, however, 

 readily converted by the digestive ferments and juices into pep- 

 tones, and thus dissolved. 



F. Peptone. 



This substance is formed by the action of the digestive fer- 

 ments from any of the above albumins, in the stomach by pepsin 

 in Jhe presence of dilute acid, and in the small intestines by tryp- 

 sin in the presence of dilute alkali. This change renders them 

 more soluble and diffusible, and thus enables them to pass out 

 of the alimentary canal into the system, and makes them more 

 suited to take part in the nourishment of the body. 



The leading characteristics of peptones may be thus enumer- 

 ated : 



1. Very ready solubility in hot or cold water, acids or alka- 



lies. 



2. Not coagulable by heat. 



3. They are precipitated by alcohol but not changed to the 



coagulated form. 



4. They diffuse more readily through animal membrane 



than other albumins. 



5. They are not precipitated by sulphate of copper, chloride 



of iron, or ferrocyanide of potassium and acetic acid. 



6. They are precipitated by iodine, chlorine, tannin, chlo- 



ride of mercury, and the nitrate of silver and mercury. 



7. Caustic potash and a trace of sulphate of copper added 



to their solutions give a red color which deepens to vio- 

 let if too much of the copper salt be used. 

 The formation of peptones is a gradual process having many 

 intermediate steps, in the earlier stages of which precipitates are 

 formed by ferrocyanide of potassium and acetic acid. (Vide 

 Chaps. VIII and IX and on Chemistry of Digestion.) 



