216 THE GASTRIC JUICE. 



peptone has been given. Reduced to the solid form by care- 

 ful evaporation, peptone is a white or yellowish-white sub- 

 stance; almost tasteless and inodorous; very soluble in 

 water; but insoluble in alcohol of eighty-three per cent. Its 

 watery solution reddens litmus, and is precipitated by 

 chlorine, tannic acid, and metallic salts ; but it is unaffected 

 by boiling, by acids, or by alkalies. With alkalies and bases 

 it forms very soluble neutral compounds or salts. An 

 aqueous solution of these is still less precipitable by reagents 

 than one of peptone itself. Thus it is only thrown down by 

 tannic acid, bichloride of mercury, and a mixture of the 

 acetates of ammonia and lead : the acetate of lead, and the 

 ferrocyanide of potassium, causing but a faint cloudiness ; and 

 even concentrated acids, nitrate of silver and alum, having no 

 effect* 



The gastric juice dissolves, as we have seen, only the albu- 

 minoid constituents of food; it is therefore evident that a 

 much greater proportion of these constituents is digested in 

 the stomach of carnivorous than herbivorous animals. Hay 

 contains only about 7 per cent, of albuminoid constituents, 

 and it is these alone which are acted upon by the gastric 

 juice in the stomach. The gastric juice helps, to a certain 

 extent, the solution of solid animal fats, by dissolving the 

 nitrogenous walls of the cells which contain the fat, and also 

 the digestion of starch by dissolving the walls of the veget- 

 able cells containing it. The gastric juice has, however, no 

 action on the fatty and starchy constituents proper of the 

 food. 



It remains for us to examine the action which the gastric 

 juice has on certain remedies taken into the stomach, and to 

 consider the reasons why this fluid, which out of the body 



* On Food and its Digestion. By Dr BRINTON. Page 125. 



