DIGESTION. 163 



be observed by means of a gastric fistula. A metallic catheter, intro- 

 duced through the fistula when the stomach is empty, must usually 

 be held in place, or it will fall out by its own weight. But on the 

 introduction of food, the catheter is grasped and retained with some 

 force, by the contraction of the muscular coat. A twisting motion 

 of its extremity may also be frequently observed, similar to that 

 described by Beaumont. This peristaltic action, though quite gentle, 

 is sufficient to produce a churning movement of the food, by which its 

 different portions are shifted from side to side, and the gastric juice 

 made to penetrate thoroughly all its parts. It thus receives a more 

 rapid and uniform digestion of its various ingredients. The move- 

 ment is one which cannot be fully imitated in experiments on artificial 

 digestion in test-tubes ; and the process, under these circumstances, is 

 consequently less rapid than in the interior of the stomach. 



The alimentary matters, thus incorporated with the gastric juice, are 

 disintegrated by the liquefaction of their albuminous ingredients. 

 Bread consists mainly of hydrated starch and solid gluten. By diges- 

 tion the gluten is converted into soluble peptone, the starch being 

 thus set free, and the whole reduced to a diffluent condition. The 

 same effect is produced on bread subjected to the action of gastric 

 juice in a test-tube, the gluten passing into a liquid condition, while 

 a deposit of unaltered starch settles at the bottom. Cheese, consisting 

 of coagulated caseine and milk globules, undergoes an analogous change. 

 Its caseine is liquefied, while its liberated fat globules rise to the upper 

 part of the fluid, forming a creamy-looking layer on its surface. 



Adipose tissue is disintegrated by the liquefaction of its fibrous and 

 membranous parts, while the fatty matter escapes in the form of oil 

 drops, floating upon the other contents of the stomach. Beaumont 

 always found free oil globules, thus extricated from the fatty tissues 

 soon after they had been taken with the food ; and it is easy to verify 

 this observation, either by artificial digestion of adipose tissue in 

 gastric juice, or by opening the stomach of an animal after the admin- 

 istration of food containing fat. 



The digestion of muscular Jlesh is also at first a process of disin- 

 tegration. The connective tissue surrounding the fibrous bundles 

 yields to the action of the gastric juice, and the fibres become sepa- 

 rated, forming a gruelly mixture of microscopic threads and fragments. 

 The fibres then break up, and, when examined by the microscope, are 

 found to have lost the distinctness of their transverse striations. In 

 food which has been thoroughly masticated, this change goes on rap- 

 idly and uniformly throughout the mass. If, as in the dog, the meat 

 be swallowed without much mastication, or if portions be suspended 

 in a test-tube with gastric juice, the digestive action progresses from 

 without inward. The external parts are first softened and decolorized, 

 becoming covered with a grayish layer, of grumous consistency, con- 

 taining the isolated fragments of muscular fibre. As these portions 

 are removed, the action extends to the parts beneath, and so on until 



