388 CHANGES IN THE STOMACH. [Boon 11. 



mouth of the horse is insufficient to produce any marked con- 

 version of the starch it may contain. During the rapid transit 

 through the oesophagus no appreciable change takes place. 



The amount of absorption of digested material, or even of 

 simple water from the mouth or oesophagus, must always be 

 insignificant. 



The Changes in the Stomach. 



229. The arrival of the food, the reaction of which is either 

 naturally alkaline, or is made alkaline, or at least is reduced in 

 acidity, by the addition of saliva, causes a flow of gastric juice. 

 This, already commencing while the food is as yet in the mouth, 

 increases as the food accumulates in the stomach, and as, by the 

 churning gastric movements, one part after another of the food 

 is brought into contact with the mucous membrane. 



The characters of the juice appear to change somewhat as the 

 act of digestion proceeds. The amount of pepsin in the gastric 

 contents increases for some time after food is taken, and prob- 

 ably the actual secretion increases also. The acidity of the 

 gastric contents is at first very feeble ; indeed in man, in some 

 cases at least, for some little time after the beginning of a meal 

 no free acid is present, and during this period the conversion of 

 starch into sugar may continue. This condition however is 

 temporary only ; very soon the contents become acid, arresting 

 the action of and ultimately destroying the amylolytic ferment ; 

 and, since the rate of the secretion of acid appears to be fairly 

 constant, the contents of the stomach, unless fresh alkaline food 

 be taken, become more acid as digestion goes on. 



The gross effect of gastric digestion is to break up and partly 

 to dissolve the larger lumps of masticated food into a thick 

 greyish soup-like liquid called chyme, with which are still mixed 

 in variable quantity larger and smaller masses of less changed 

 food. This is the result, partly of the solution of proteid mat- 

 ters, partly of the solution of the gelatiniferous connective-tissue 

 holding the proteid elements together. In a fragment of meat, 

 for instance, the muscular fibres, through the solution, of the 

 connective-tissue binding them together, fall asunder, the sarco- 

 lemma is dissolved, and the fibres themselves split up sometimes 

 longitudinally but most frequently by transverse cleavage into 

 discs, and are ultimately more or less reduced partly into a 

 granular mass, partly to actual solution. In a piece of tissue 

 containing fat, the connective-tissue binding the fat cells 

 together and the envelopes of the fat cells are dissolved, so that 

 the fat, fluid at the temperature of the body, is set free from 

 the individual cells and runs together into larger and smaller 

 masses. In vegetable tissue the proteid elements are in part 

 dissolved and, though there is no evidence that in man cellulose 



