CHAPTER XLVII 

 DIGESTION IN THE SMALL INTESTINE 



AFTER being churned to a proper fluid consistency in the pyloric 

 mill, and having attained to a certain degree of acidity, the gastric 

 contents little by little are passed through the pyloric aperture, and 

 enter as a chyme the first part of the small intestine. This is the short, 

 horseshoe -shaped duodenum. It is the acidity of the chyme in the 

 pylorus which excites the relaxation of the pyloric aperture. On 

 reaching the duodenum, the acidity of the chyme causes the door 

 behind it to shut, and prevents regurgitation into the stomach. The 

 chyme contains 



1. Such sugars, starches, and proteins as have not been acted 

 upon by the salivary or peptic ferments. 



2. Acid, free and combined. 



3. Proteoses and peptones. 



4. Rancid fat. 



On its entrance into the duodenum, a number of important events 

 are brought to pass : 



1. A flow of bile is provoked from the gall-bladder. 



2. The acid contained in the chyme liberates from the duodenal 

 mucous membrane the hormone " secretin," which, circulating in 

 the blood, calls forth a flow of digestive juice from the pancreas and 

 a further flow of bile from the liver. 



3. The presence of the chyme in the intestines, probably owing to 

 its acidity and the nature of its contents, causes a flow of succus enteri- 

 cus the digestive fluid of the small intestine. 



On these three fluids the bile, pancreat'c juice, and succus 

 entericus depends the proper digestion of the entering foodstuffs. 



THE BILE. This varies in appearance and composition according 

 to its source. Bile from the gall-bladder is a ropy, viscid substance, 

 bitter to taste, faintly alkaline in reaction, with a specific gravity from 

 1015 to 1040. Its colour in man varies from yellow to green. Bile 

 obtained from the liver before entering the gall-bladder is a clear, 

 limpid fluid of low specific gravity (1010), pale yellow in colour. In 

 the gall-bladder, water is absorbed varying in amount according to 

 the time of stay, and a mucous lecretion is added. The protein in this 

 secretion in most animals mainly consists of phospho-protein. In 

 man, however, it is stated to be true glyco-protein. The difference 

 between the two kinds of bile is shown in the following analysis: 



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