472 CHANGES IN THE STOMACH. [BOOK n. 



the whole tissue is softened and to a certain extent disintegrated. 

 Milk is curdled and the curd subsequently more or less dissolved. 



The thick soup-like acid chyme consists accordingly partly of 

 substances which have entered into actual solution, partly of mere 

 particles or droplets of proteid, fatty or other nature and partly of 

 masses small op great, which may be recognized under the micro- 

 scope as more or less changed portions of animal or vegetable 

 tissue. The amount of material actually dissolved is in most 

 specimens of chyme exceedingly small. When the solid parts are 

 removed by nitration the clear filtrate contains besides salts, pepsin 

 and free hydrochloric acid (the constituents of the gastric juice), a 

 small amount of sugar, of parapeptone and of peptone. The sugar 

 is often absent, the parapeptone is not always present, and the 

 amount of peptone (or albumose) is always small. 



During gastric digestion the chyme thus formed is from time 

 to time ejected through the pylorus, accompanied by even large 

 morsels of solid less-digested matter. This may occur within a 

 few minutes of food having been taken; but the larger escape 

 from the stomach probably does not in man begin till from one to 

 two, and lasts from four to five hours, after the meal, becoming 

 more rapid towards the end, and such pieces as are the least 

 broken up by the gastric juice and movements being the last to 

 leave the stomach. 



The time taken up in gastric digestion probably varies in the 

 same animal not only with different articles of food but also with 

 varying conditions of the stomach and of the body at large. In 

 different animals it varies very considerably, being from 12 to 24 

 hours in the dog after a full meal, while the stomachs of rabbits 

 are never empty but always remain largely filled with food, even 

 during starvation. In man the stomach probably becomes empty 

 between the usual meals. 



The total amount of change which the food undergoes in the 

 stomach, that is the share taken by the stomach in the whole 

 work of digestion, seems to vary largely in different animals, and 

 in the same animal differs according to the nature of the meal. 

 In a dog fed on an exclusively meat diet, a very large part of the 

 digestion is said to be carried out by the stomach, very little work 

 apparently being left for the intestines ; that is to say, the larger 

 part of the meal is reduced in the stomach to actual solution and 

 a considerable quantity is probably absorbed directly from the 

 stomach. In such cases the amount of peptone found in the 

 stomach during the digestion of the meal is found to be fairly 

 constant, from which it may be inferred that the peptone is absorbed 

 as soon as it is formed. There is also evidence that fat may to 

 a certain extent undergo in the stomach changes leading to 

 emulsion, similar to those which, as we shall see, are carried out 

 in the small intestine. 



But such cases as these cannot be regarded as typical cases of 



