3<D2 



ESSENTIALS OF PHYSIOLOGY. 



of mucous membrane is taken into consideration ; moreover, it has the 

 advantage of being free from admixture with food. 



The juice obtained in this way is a clear fluid having a specific gravity 

 of 1003-5 and an acid reaction. It consists of about 99 per cent, 

 of water and 1 per cent, of solids, the latter including mucin, proteins, 

 enzymes, and inorganic salts. The juice also contains free hydrochloric 

 acid in the proportion of about 0'2 per cent, in man; the percentage is 

 I. II. 



Right vagus. 



Peritoneal coat. 

 Muscular coat. 



Mucous membrane. 



FIG. 119. Pawlow's method of forming a subsidiary stomach. (From]Pawlow's 



Work of the Digestive Glands.} 

 I., first stage : A B, incision. II., lesser stomach completed : S, lesser stomach ; A, abdominal wall. 



rather higher in the dog and other carnivorous animals. The salts are 

 chiefly chlorides and phosphates of potassium, sodium, calcium, and 

 magnesium, the base in largest proportion being potassium. 



The existence of free hydrochloric acid may be proved by two tests : (1) 

 A solution of Congo red added to gastric juice gives a blue colour, showing 

 the presence of free mineral acid. (2) If a drop of Gunzberg's reagent 

 (phloroglucin- vanillin) be evaporated to dryness and a drop of gastric juice 

 be added to the residue and gently heated, as drying takes place a bright red 

 colour is developed, proving that the acid is hydrochloric. 



THE FUNCTIONS OF THE GASTRIC JUICE. 



It has already been pointed out that the acid of the gastric juice 

 destroys the ptyalin of the saliva, but the hydrolysis of the carbo- 

 hydrates of the food may be continued, to some extent at least, by the 

 hydrochloric acid in the stomach. This chemical hydrolysis, however, 

 if it occurs, is of less importance than the action of the gastric enzymes 

 upon proteins, milk, and fats. 



The digestive action of gastric juice can be studied, -like that*of 

 saliva, by means of experiments in test tubes. Fresh gastric juice 

 obtained from a fistula may be used, but it is generally more con- 

 venient to make an artificial extract. For this purpose the mucous 

 membrane of a pig's stomach is cut in small pieces and extracted 



