' DIGESTION IN THE STOMACH 689 



THE EFFECT OF GASTRIC JUICE ON CARBOHYDRATES 



On account of the fact that cane sugar undergoes inversion into equal 

 molecules of glucose and fructose in the stomach, it has been sometimes 

 thought that gastric juice contains a ferment invertase. It seems, however, 

 that the inversion which takes place in the stomach can be completely 

 accounted for by the action of hydrochloric acid present, and that there is no 

 need to assume the presence of a special ferment. 



In the same way inulin, the variety of starch which gives rise to the 

 Isevorotatory sugar fructose on hydrolysis, and is found in dahlia tubers and 

 certain other reserve structures of plants, is converted by the acid of gastric 

 juice into fructose. The inulin is therefore completely utilised in the ali- 

 mentary canal of animals, although there is no definite ferment inulase 

 provided for its hydrolysis. 



THE EFFECT OF GASTRIC JUICE ON FATS 



The chief action of this juice on fats is the solution of their connective- 

 tissue framework and protoplasmic envelopes, so as to set the fat free in the 

 stomach contents. After a fatty meal it is found moreover that a consider- 

 able proportion of the fat in the stomach has undergone hydrolysis and con- 

 version into free fatty acid. In this hydrolysis two factors are involved, viz. 

 (1) the action of the warm dilute hydrochloric acid ; (2) the action of a 

 special fat-splitting ferment or lipase, which is secreted by the walls of the 

 stomach, and acts especially at the beginning of gastric digestion before the 

 contents have attained a high degree of acidity. The action of this ferment 

 is only marked if the fat be present in a finely divided form, e.g. as yolk of 

 egg. The chief digestion of fat takes place in the next segment of the 

 alimentary canal, namely, in the duodenum. 



THE SECRETION OF GASTRIC JUICE 



Pawlow has shown that if an animal provided with gastric and cesophageal 

 fistulae be given food, when hungry, it will eat with avidity, and since the 

 food cannot reach the stomach and so satisfy its hunger, it will continue to 

 eat for two or three hours. Five minutes after the beginning of this sham 

 feeding, gastric juice begins to drop from the fistulous opening ; and in this 

 way large quantities of juice, free from any admixture with other substances, 

 can be easily obtained. By this means we obtain a secretion of gastric juice, 

 which is excited by the presence of food in the mouth. This method does not, 

 however, enable us to determine whether the character of the juice will be 

 altered in any way by the changes which the food undergoes in the stomach 

 itself. In order to form an idea of the normal course of secretion of gastric 

 juice, when food is taken into the stomach in the ordinary way, Pawlow has 

 devised another procedure. A small diverticulum representing about one- 

 tenth of the whole stomach is made at the cardiac or pyloric c\nd, in direct 

 muscular and nervous continuity with the rest of the stomach, but shut off 

 from the main part of the viscus by a diaphragm of mucous membrane. The 

 method in which this operation is carried out will be evident by reference to 



