400 A TEXTBOOK OF PHYSIOLOGY 



Steapsin, in the presence of bile, acts upon the finely emulsified 

 iats, and converts them into glycerine and fatty acid (see p. 71). 



Lecithin is hydrolyzed to glycerine, fatty acid, and choline. It 

 is not clear what part rennin can play, as all ingested milk is curdled 

 in the stomach. 



The nvtclease present splits nucleic acid into purin bodies. In 

 cases of pancreatic disease, it is stated that, owing to the absence of 

 trypsin and nuclease, the cell-nuclei in the food are not disintegrated, 

 and therefore pancreatic disorder can be traced by examining the 

 faeces after a meal rich in cell nuclei, such as sweetbreads. 



THE SUCCUS ENTERICUS. This is secreted by the tubular 

 glands lining the small intestines, and also by the glands of Brunner. 

 To obtain the juice, a piece of the intestine is isolated with the 

 mesentery intact, and the two open ends are sewn into the abdominal 

 walls the severed ends of the intestine are reunited (Vella's method), 

 or one end only of the isolated piece of the intestine is sewn into the 

 abdominal wall, the other being sutured (Thiry's method). Such fistulae 

 have been established in man by operations undertaken to relieve 

 strangulated hernia, etc. In either case, the juice can be removed 

 from the loop and tested in vitro, or food can be introduced into 

 the loop, and afterwards removed and examined. 



Obtained in this way, the succus entericus is a yellowish, turbid, 

 viscid fluid, alkaline in reaction, with a specific gravity of 1007 to 1010, 

 and a solid content of about 1-5 per cent. The viscidity is probably 

 due to a body of the iiucleo -protein type, rather than to a true mucin 

 (gluco-protein). It plays an important part in protecting the intestine 

 and facilitating the movements of the intestinal contents. The juice 

 also contains a small amount of serum albumin and globulin, and 

 certain enzymes erepsin, invertase, maltase, and a feeble lipase. 

 In animals taking milk, a lactase is also present. In addition, it 

 contains enterokinase. The chief salts are sodium chloride and 

 carbonate. The glands of Brunner in the duodenum secrete a pepsin- 

 like enzyme; also in herbivora a diastatic enzyme. 



The intestinal secretion reaches its maximum about three hours 

 after food, continuing for six to eight hours. It is greater in the 

 upper than in the lower part of the intestine. It is stated to 

 average in the dog about 100 c.c. daily, in man from 150 to 300 c.c., 

 but it is very difficult to give accurate figures. 



The Mechanism of the Secretion. The mucus comes mainly from 

 the goblet cells, the rest of the secretion from the other cells of the 

 glands. The granules of these increase during rest, and diminish 

 during activity. The juice is secreted in the upper part of the intes- 

 tine in response to the presence of hydrochloric acid in the gut, but 

 whether it is due to the direct excitation of the cells or to a " hormone " 

 mechanism is not definitely decided. In regard to the secretion in the 

 lower part, it seems probable that this is determined by the absorption 

 of the products of digestion higher up, and it may be that it varies in 

 composition and amount according to the nature of the food absorbed. 



