DIGESTION. 681 



rendered feebly alkaline and mixed with 2 c.o. of a 1 per cent, 

 solution of calcium chloride and 10 c.c. of milk. If the rennin 

 zymogen be present, a heavy cake of casein is precipitated in a few 

 minutes. 



1. 'Detection of proteins. Of these, syntonin, albumoses, and pep- 

 tones are to be looked for. Syntonin : The gastric filtrate is exactly 

 neutralized, whereupon a cloudiness or precipitate is formed, which 

 is soluble both in alkalies and in acids. Albumoses: These are pre- 

 cipitated by a saturated solution of ammonium sulphate, while pep- 

 tones remain in solution. Peptones : These are recognized by the 

 biuret-test. The juice is rendered strongly alkaline with potassium 

 hydroxide and a few drops of a cupric sulphate solution (1 in 1000) 

 are added. A red color indicates the presence of peptones. 



ra. Detection of carbohydrates. Starch is recognized by the blue 

 color produced by iodine solution (1 iodine, 2 potassium iodide, 100 

 water). The reaction is less marked in proportion to the amount of 

 starch converted into dextrin and sugar. 



Erythrodextrin gives a mahogany-brown color, and achroodextrin 

 remains unchanged by the iodine solution. Inasmuch as sugar is 

 present in the test-meal itself, it is useless to test for this substance. 



Intestinal digestion. The changes in food taking place in the 

 small intestine are much more complex and far-reaching than those 

 occurring in the stomach. Little or no absorption takes place from 

 the stomach, and the alterations in the food brought about by the 

 gastric juice can be considered as being largely preparatory for the 

 action of the digestive fluids of the intestine. The close dependence 

 of one part of the process of digestion on the other is shown by the 

 normal effect of the entrance of chyme into the duodenum. The 

 acid chyme causes a reflex secretion of the pancreatic juice, the bile, 

 and the intestinal juice, the digestive fluids of the intestine. These 

 fluids are all alkaline, and are secreted in sufficient quantity to neu- 

 tralize the chyme and to provide the degree of alkalinity most suit- 

 able for the action of the ferments which complete the process of 

 digestion. A slight increase of the acidity of the gastric contents is 

 followed by an increase in the secretion of the digestive fluids of the 

 intestine. Intestinal digestion depends upon three secretions : (1) 

 the pancreatic juice ; (2) the bile ; (3) the succus entericus, the secre- 

 tion of the intestine. 



Pancreatic secretions. The secretions of the pancreas are of 

 two kinds, an external, the pancreatic juice, which flows into the 



