CH. XXXI.] 



ACTION OF GASTRIC JUICE. 



485 



They give the biuret reaction (rose-red solution with a trace of 

 copper sulphate and caustic potash or soda). 



Peptone is readily diffusible through animal membranes. The 

 utility of the formation of diffusible substances during digestion 

 is obvious. 



Proteoses. These are the intermediate products in the 

 hydration of native proteids into peptones. 



They are not coagulated by heat ; they are precipitated but 

 not coagulated by alcohol : like peptone they give the biuret 



reaction. They are precipitated by nitric acid, the precipitate 

 being soluble on heating, and reappearing when the liquid cools. 

 This last is a distinctive property of proteoses. They are slightly 

 diffusible. 



The above table will give us at a glance the chief characters 

 of peptones and proteoses in contrast with those of the native 

 proteids, albumins, and globulins. 



We see that the main action of the gastric juice is upon the 

 proteids of the food, converting them into more soluble and 



* In the caw of deutero-albumose this reaction only occurs in the presence 

 of excess of salt. 



