ALBUMINOIDS. 63 



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 ferments 

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

 presence of dilute acid, and in the small intestines by trypsin 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 enumerated : 



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 readily through animal membrane. 



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



of iron, or ferro-cyanide of potassium and acetic acid. 



6. They are precipitated by iodine, chlorine, tannin, chloride 



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 violet 

 if too much of the copper salt be used. 



The formation of peptones is a gradual process having many in- 

 termediate steps, in the earlier stages of which, precipitates are 

 formed by ferro-cyanide of potassium and acetic acid. (Vide 

 Chaps. VIII. and IX. and on Chemistry of Digestion, pp. 131 and 

 141.) 



Group III. ALBUMINOIDS. 



These are the outcome of nutritive modification of protoplasm, 

 and may be said to be directly manufactured by that substance, 

 and to be specially adapted to meet the requirements of certain 

 textures differing widely in function. They are allied to one 

 another and to the last group by (a) their percentage composi- 



