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TEXT-BOOK OF PHYSIOLOGY 



thoracic duct. Because of the general belief that the lymph-capillaries 

 were in open communication with the tissue spaces it was assumed that 

 the absorption of lymph and its flow through the lymph-vessels was the 

 result of a difference of pressure between the lymph in the tissue spaces and 

 the blood in the innominate veins. But if the lymph-capillaries are closed 

 vessels, as recent investigations indicate, then additional factors, in explana- 

 tion of lymph absorption, must be sought for. 



It is quite possible under even normal conditions of pressure in the tissue 

 spaces that some of the more diffusible constituents of the lymph are 



absorbed by the capillary blood-vessels. As 

 to whether the relatively feebly diffusible 

 colloids are so resorbed is as yet a matter of 

 investigation. 



ABSORPTION OF FOODS 



The most important of the absorbing sur- 

 faces, especially in its relation to the absorp- 

 tion of new material, is the mucous mem- 

 brane of the alimentary canal, and more par- 

 ticularly that portion lining the small intestine, 

 provided as it is with specialized absorbing 

 structures the villi. Though certain sub- 

 stances can be absorbed from the mouth, it 

 is not probable that any food is so absorbed. 

 From the changes which the food principles 

 undergo in the stomach it might naturally be 

 inferred that their absorption would promptly 

 follow. Experimental researches have demon- 

 strated, however, that this takes place, if at 

 all, but to a slight extent. If, however, solu- 

 FIG. 86.-LoNGiTUDiNAL SEC- tions of ^organic salts, sugars, and peptones 

 TION OF A VILLUS FROM INTESTINE possessing a concentration of at least 5 per 

 OF THE DOG. HIGHLY MAGNIFIED. cen t. a degree of concentration seldom re- 

 goblet^ur^randm^raSry^eu- alized under normal conditions are intro- 

 kocytes (h). c. Basement mem- duced into the stomach, their absorption will 



brane. <*. Plate-like connective- be effected, the rate of absorption following in 

 tissue elements of core. e. e, . r .,,.,.., . 



Blood-vessels. /. Absorbent radi- a general way the increase, within limits, in 

 cal or lacteal. (Piersol.) concentration. Water is practically not ab- 



sorbed from the stomach. The absorption 



of the products of digestion i.e., dextrose, levulose, peptones, amino-acids, 

 soaps, glycerin, fat acids, salts, along with water, in which for the most 

 part they are held in solution is therefore limited very largely to the 

 small intestine, and is accomplished by the villous processes projecting 

 from the surface of the mucous membrane. 



Structure of the Villi. The villi are small filiform or conical processes, 

 from 0.5 to i mm. in length, and from 0.2 to 0.5 mm. in breadth, covering 

 the surface of the mucous membrane from the pyloric orifice to the upper 

 surface of the ileo-cecal valve. Each villus consists of a basement mem- 

 brane (see Fig. 86) supporting tall columnar epithelial cells. Each cell is 



a, 



