22 2 TEXT-BOOK OF PHYSIOLOGY. 



storage and liberation of energy. It may also be regarded as a 

 reservoir for the reception of all those compounds which arise from 

 tissue metabolism prior to their removal by the blood-vessels and 

 lymphatics. 



Absorption of Lymph. The production of lymph is apparently 

 a continuous process, and as a result there is more lymph passing 

 through the capillary vessels than is necessary for the immediate needs 

 of the tissues.^ Should this accumulate, there would arise the con- 

 dition ef-edgma and an interference with the functional activity of 

 the tissues.^ As soon as a certain pressure arises in the tissue spaces 

 there is a movement of the lymph into the lymph- capillaries and 

 vessels toward the termination of the thoracic duct, where the pres- 

 sure is relatively low. In consequence of this difference in pressure 

 the lymph is withdrawn from the tissues. 



It is quite possible under even normal conditions of pressure in 

 the tissue spaces that some of the more diffusible constituents of the 

 lymph should be absorbed by the capillary blood-vessels. As to 

 whether the relatively feebly diffusible colloids should be so resorbed 

 is as yet a matter of investigation. 



ABSORPTION OF FOODS. 



The most important of the absorbing surfaces, especially in its 

 relation to the absorption of new material, is the mucous membrane 

 of the alimentary canal, and more particularly that portion lining the 

 small intestine, provided as it is with specialized absorbing structures 

 the villi. Though certain substances 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 demonstrated, however, that this takes 

 place, if at all, but to a slight extent. If, however, solutions of inor- 

 ganic salts, sugars, and peptones possessing a concentration of at 

 least 5 per cent. a degree of concentration seldom realized under 

 normal conditions are introduced into the stomach, their absorption 

 will be effected, the rate of absorption following in a general way the 

 increase, within limits, in concentration. \WVater is practically not 

 absorbed from the stomach.^ The absorption of the products of 

 digestion i. e., dextrose, levulose r peptones, soaps, glycerin, fatty 

 acids, salts, along with water, in which for the most part they are 

 held in solution is therefore limited very largely to the small intes- 

 tine, 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 



