388 GASTRIC JUICE. [BOOK n. 



and removed the remainder by evaporation at a low temperature, 

 to cover the pieces of gland with strong glycerine. Though some 

 of the ferment appears to be destroyed by the alcohol a mere drop 

 of such a glycerine extract rapidly converts starch into sugar. 



Gastric Juice. 



201. There is no difficulty in obtaining what may fairly be 

 considered as a normal saliva ; but there are many obstacles in the 

 way of determining the normal characters of the secretion of the 

 stomach. When no food is taken the stomach is at rest and no 

 secretion takes place. When food is taken, the characters of the 

 gastric juice secreted are obscured by the food with which it is 

 mingled. The gastric membrane may it is true be artificially 

 stimulated, by touch for instance, and a secretion obtained. This 

 we may speak of as gastric juice, but it may be doubted whether 

 it ought to be considered as normal gastric juice. And indeed as 

 we shall see even the juice, which is poured into the stomach 

 during a meal, varies in composition as digestion is going on. 

 Hence the characters which we shall give of gastric juice must be 

 considered as having a general value onty. 



Gastric juice, obtained in as normal a condition as possible 

 from the healthy stomach of a fasting dog, by means of a gastric 

 fistula, is a thin almost colourless fluid with a sour taste and 

 odour. 



In the operation for gastric fistula, an incision is made through the 

 abdominal walls, along the linea alba, the stomach is opened, and the 

 lips of the gastric wound securely sewn to those of the incision in the 

 abdominal walls. Union soon takes place, so that a permanent opening 

 from the exterior into the inside of the stomach is established. A tube 

 of proper construction, introduced at the time of the operation, becomes 

 firmly secured in place by the contraction of healing. Through the 

 tube the contents of the stomach can be received, and the mucous 

 membrane stimulated at pleasure. 



When obtained from a natural fistula in man, its specific 

 gravity has been found to differ little from that of water, varying 

 from 1*001 to I'OIO, and the amount of solids present to be 

 correspondingly small. In animals, pure gastric juice seems to be 

 equally poor in solids, the higher estimates which some observers 

 have obtained being probably due to admixture with food, &c. 



Of the solid matters present about half are inorganic salts, chiefly 

 alkaline (sodium) chlorides, with small quantities of phosphates. 

 The organic material consists of pepsin, a body to be described 

 immediately, mixed with other substances of undetermined nature. 

 In a healthy stomach gastric juice contains a very small quantity 

 only of mucin, unless some submaxillary saliva has been swallowed. 



