THE ABSORPTION OF THE FOOD-STUFFS 



827 



absorption is still possible. The introduction of water into the 

 stomach simply increases the dilatation, but does not relieve the 

 intense thirst of the patient. Water that has been swallowed to 

 quench thirst has first to be passed from the stomach into the small 

 intestine before it can be absorbed and relieve the needs of the tissues. 

 The intestinal contents at the ileocaecal valve contain relatively 

 nearly as much water as they do at the upper part of the jejunum. 

 Their absolute bulk is, however, much smaller, so that only a small 

 proportion of the water that has been taken in by the mouth remains 

 to be absorbed in the large gut an amount probably much less 



Central lacteal 



Epithelium of 



VJllllr 



Vein 



Artery 



Lieberkiihn's 



follicle 



It I 



Mucosa 

 iluscularis muc. 



Submucosa 

 Lymphatic plexus 



Circular muscle 



Lymphatic plexus 

 Longitudinal muse. 



FIG. 347. Diagrammatic section through wall of small intestine to show 

 vascular and lymphatic arrangements of mucous membrane. (From 

 BOHM and DAVIDOFF after MALL.) 



than that which has been added to the contents of the small intestine 

 in the form of secretion by the stomach, liver, pancreas, and intestinal 

 tubules. 



The main problem before us is therefore the mechanism of absorp- 

 tion of water and saline fluids by the villi of the small intestine. 

 By means of these structures the absorbing surface of the intestine 

 is largely increased. It has been calculated that each square milli- 

 metre of intestine represents an absorbing surface of 3 to 12 mm. 2 

 Each villus (Fig. 347) consists of a framework of reticular tissue con- 

 taining many leucocytes in its meshes, separated from the lumen of 

 the gut by a continuous layer of columnar epithelial cells. These cells 

 rest on an incomplete basement membrane and present on the side 

 turned towards the lumen of the gut a striated basilar border. The 

 villus offers two channels by means of which material, which has 

 passed through the epithelium, may be carried into the general 



