PEPTIC DIGESTION 57 



or food. The main facts in relation to this pure juice are as 

 follows : — It is clear and colourless ; it has a specific gravity of 1003 to 

 1006. It is feebly dextro-rotatory, gives no bitiret reaction, but gives 

 the ordinary proteid reactions. It contains from 04 to 0'6 per cent, 

 of hydrochloric acid. It is strongly proteolytic, and inverts cane 

 sugar. When cooled to 0° C. it deposits a fine precipitate of pepsin ; 

 this settles in layers, and the layers first deposited contain most of 

 the acid, which is loosely combined with and carried down by the 

 pepsin. Pepsin is also precipitable by saturation with ammonium 

 sulphate (Kuhne). Elementary analysis gave the following results : — 



More recently Pawlow has by a very ingenious surgical operation 

 succeeded in the dog in separating ofif from the stomach a diverticulum 

 which pours its secretion through an opening in the abdominal wall. 

 The folloA\"ing are his main results : — 



1. Increase in the quantity of food given causes an increase in 

 the amount of gastric juice secreted. 



2. The juice is most abundant in the early periods of digestion, 

 but it continues to be secreted in declining quantity as long as any 

 food remains to be dealt with. When there is no food given there 

 is no juice. But sham feeding or chewing will cause it to flow. 



3. The amount of pepsin secreted is similarly proportional to the 

 needs of the animal. 



4. The larger the proportion of proteid in the diet, the more 

 abundant and active is the juice secreted. 



THE ACTION OF GASTRIC JTTICE 



The principal actions of the gastric juice have been already 

 practically studied : the action of pepsin in converting the proteids 

 of the food into the diffusible peptones is its chief action. The 

 curdling of mUk by rennet will be fotmd described in Lesson TV. 



There is a still further action— that is, the gastric juice is anti- 

 septic ; putrefactive processes do not normally occur in the stomach, 

 and the organisms that produce such processes, many of which are 

 swallowed with the food, are in great measure destroyed, and thus 

 the body is protected from them. The acid is the agent in the juice 

 that possesses this power. 



