240 GASTRIC JUICE. [BOOK IT. 



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 rOOl to TO 10, 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 mucus, unless some submaxillary saliva has been swallowed. 



The reaction is distinctly acid, and the acidity is normally due 

 to free hydrochloric acid. This is shewn by various proofs, among 

 which we may mention the fact that the amount of hydrochloric 

 acid is more than can be neutralized by the bases, and the excess 

 corresponds to the quantity of free acid present. Lactic and 

 butyric and other acids when present are secondary products, 

 arising either by their respective fermentations from articles of 

 food, or from the decomposition of their alkaline or other salts. In 

 man the amount of free hydrochloric acid in healthy juice may 

 be stated about '2 per cent., but in some animals it is probably 

 higher. 



On starch gastric juice has per se no effect whatever ; indeed 

 the acidity of the juice tends to weaken, or may be sufficient to 

 arrest and even destroy, the amylolytic action of any saliva with 

 which it may be mixed. 



On dextrose healthy gastric juice has no effect. And its power 

 of inverting cane-sugar seems to be less than that of hydrochloric 

 acid diluted to the same degree of acidity as itself. In an un- 

 healthy stomach however containing much mucus, the gastric 

 juice is very active in converting cane-sugar into dextrose. This 

 power seems to be due to the presence in the mucus of a special 

 ferment, analogous to, but quite distinct from, the ptyalin of 

 saliva. An excessive quantity of cane-sugar introduced into 

 the stomach causes a secretion of mucus, and hence provides for 

 its own conversion. 



On fats gastric juice has at most a limited action. When 

 adipose tissue is eaten, the chief change which takes place in the 

 stomach is that the proteid and gelatiriiferous envelopes of the 

 fat-cells are dissolved, and the fats set free. Though there is 

 experimental evidence that emulsion of fats to a certain extent 



