130 NUTRITIONAL PHYSIOLOGY 



unchanged volume. Some poisons produce no positive 

 effects while in the stomach, but exert their action promptly 

 when they pass to the small intestine. 



As regards the sugars and the products of peptic diges- 

 tion, it is now believed that there is a considerable absorp- 

 tion of these substances from the stomach. They disap- 

 pear most rapidly when they are present in high concentra- 

 tion, and the process is promoted by condiments which 

 increase the blood flow under the gastric mucous mem- 

 brane. When all reasonable allowance is made for the 

 part played by the stomach in absorption, the fact remains 

 undisputed that the major part of the work is done below 

 the pylorus. Furthermore, since, as has been said, there 

 is usually little valuable material left to be recovered by the 

 colon, it becomes evident that the small intestine is of 

 central importance. 



A striking peculiarity of the small intestine is the _e_x- 

 tension of its internal surface. This is effected, first, by 

 the numerous cross-folds which cut into its cavity, and, 

 second, by the microscopic projections which stud its 

 lining. These are the villi. An individual villus may be 

 described as a minute finger-shaped process. It rises 

 above the general surface in a contrast to the glands, which 

 sink below; the villus is a peg, as the gland is a pit. Ob- 

 viously the existence of the villi increases many times over 

 the number of cells in contact with the intestinal contents. 

 These cells are described as columnar; they are prisms 

 standing side by side, with their larger surfaces in contact 

 and their smaller ends presented to the interior of the in- 

 testine and to the loose internal tissue of the villi. A 

 certain share of absorption may take place through the 

 crevices between the cells, but the main transfer of material 

 seems to be through their own protoplasmic bodies. 



The interior of a villus is filled by a confusing assortment 

 of cells, some of which have been thought to be contractile. 

 There are probably intervals between these cells containing 

 lymph, and near the central axis of the villus is a rather 

 definite lymphatic channel. It is a small branch of the 



