170 DIGESTION. 



By examining in this wa} T , from time to time, the intestinal fluids, it 

 becomes manifest that the action of the gastric juice, in the digestion 

 of albuminous substances, is not confined to the stomach, but con- 

 tinues after the food has passed into the intestine. About half an 

 hour after the ingestion of a meal, the gastric juice begins to pass into 

 the duodenum, where it may be recognized by its strongly-marked 

 acidity, and by its peculiar action, already described, in interfering with 

 Trommer's test for glucose. It has accordingly already dissolved some 

 of the ingredients of the food, and contains a certain quantity of 

 albuminose in solution. It soon afterward, as it continues to pass 

 into the duodenum, becomes mingled with the debris of muscular 

 fibres, fat vesicles, and oil drops ; substances which are easily recog- 

 nizable under the microscope, and which produce a grayish turbidity 

 in the fluid withdrawn from the fistula. By the continuous passage, 

 in this way, of the alimentary material, mixed with gastric juice, 

 through the pylorus into the intestine, the stomach becomes gradually 

 cleared of its contents. According to Dr. Beaumont the time required 

 for the entire disappearance of food from the stomach varies from one 

 hour to five hours and a half, according to the quality and quantity of 

 the material used. In the experiments of Prof. Francis G. Smith upon 

 the same subject, food seldom remained in the stomach more than two 

 hours after its introduction. Three hours is probably sufficient, as a 

 rule, for the completion of stomach digestion, in the human subject, 

 when the food is in moderate quantity and has been properly prepared 

 by cooking and mastication. In the carnivorous animals generally, 

 where the food is swallowed in fragments of some size, the process is 

 longer; and in the dog a moderate meal of fresh uncooked meat 

 requires from nine to twelve hours for its complete liquefaction and 

 disappearance from the stomach. 



The gastric juice, after having accomplished its work in the digestion 

 of the food, is reabsorbed from the alimentary canal and taken up by 

 the bloodvessels. It thus forms a vehicle for the dissolved nutritious 

 materials, and again enters the circulation with the alimentary substances 

 which it holds in solution. It is in this way that the system is enabled 

 to furnish so abundant a secretion without being exhausted by drainage. 

 The reabsorption of the gastric juice goes on simultaneously with its 

 secretion during the continuance of the digestive act; and the fluids 

 which the blood loses by one process are incessantly restored to it by 

 the other. An abundant supply, therefore, of the secretion may be 

 poured out during the digestion of a meal, at an expense to the 

 blood, at any one time, of only a small quantity of fluid. The simplest 

 investigation shows that the gastric juice does not accumulate in the 

 stomach to any considerable amount during digestion ; but that it is 

 gradually secreted so long as any food remains undissolved ; each por- 

 tion, as it is digested, being disposed of by reabsorption, together 

 with its solvent fluid. There is accordingly, during digestion, a con- 

 tinuous circulation of the digestive fluids from the bloodvessels to 



