THE CHANGES IN THE ALIMENTARY CANAL. 307 



sugar may continue. This condition, however, is temporary only; very 

 soon the contents become acid, arresting the action of and ultimately de- 

 stroying the amylolytic ferment; and, since the rate of secretion of 'acid 

 appears to be fairly constant, the contents of the stomach, unless fresh alka- 

 line 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 grayish 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 solu- 

 tion of proteid matters, partly of the solution of the gelatiniferous connec- 

 ti ve 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 sarcolemma 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 tempera- 

 ture 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 is dis- 

 solved in the stomach, the whole tissue is softened and to a certain extent 

 disintegrated. Milk is curdled and the curd subsequently more or less dis- 

 solved. 



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 or great which 

 may be recognized under the microscope 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 filtration the clear filtrate contains beside 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 para- 

 peptone 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 immediately when water alone is 

 taken and within a few minutes of food having been taken ; but the larger 

 escape from the stomach probably does not in man begin until from one to 

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

 toward 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 con- 

 ditions of the stomach and of the body at large. In different animals it 

 varies very considerably, being from twelve to twenty-four 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 



