ABSOUPTION. 



55 



of the sphincter. The act is finally accomplished, principally by a 

 contraction of the diaphragm and abdominal muscles upon a full and 

 sustained inspiration, the glottis being closed so as to prevent the 

 escape of the air contained in the lungs. 



ABSORrTION. 



Absorption is that function, by which nutritive, or other matters, 

 are taken up and carried into the circulation. There are two great 

 divisions of this function : 1st. External absorption, or the absorjotion 

 of composition, which obtains from without the organs the materials 

 intended for their composition. 2d. Internal absorption, or, the 

 absorption of decomposition, which takes up from the organs the 

 old, or effete matter that has to be replaced by new. 



By external absorption is meant that which takes place from the 

 external surface of the body, including the skin, and the mucous 

 membranes of the digestive and respiratory passages. By internal, 

 or interstitial absorption, is meant that which takes place from the 

 component tissues of the organs themselves, and from the interior of 

 shut sacs. 



The great agents of external absorption are the veins and chyli- 

 ferous vessels; of internal absorption, the lymphatics. In the chyli- 

 ferous and lymphatic vessels the fluid is always found 'to possess the 

 same general properties. In them, therefore, an action of elabora- 

 tion or selection must have taken place ; and the vital agents that 

 are concerned in this elaboration are cells. 



The veins, on the other hand, exert no selecting power, but receive 

 into their interior by imbibition, any fluid that possesses the proper 

 degree of tenuity, which is then carried along with the current of the 

 circulation. Watery fluids when taken into the stomach, in this man- 

 ner enter the circulation. Matters which find their way from the 

 stomach or intestines into the circulation, by permeating the coats of 

 the capillaries, do not pass directly from the intestinal veins into the 

 vena cava; they circulate through the liver before reaching the gene- 

 ral circulation. Magendie has observed, that in their transit through 

 the liver the properties of many substances are altered, at all events 

 they become so thoroughly mixed with the blood in their route 

 through the portal system, that their possibly injurious influence 

 upon the centre of the circulation is in a great measure, obviated. 

 Substances that require digestion, on the other hand, must pass 

 through the chyliferous vessels and thoracic duct before being mixed 

 with the blood. 



Alimentary, or digestive absorption, which is included under the 

 head of external absorption, is executed in the small intestines, and 

 is exercised upon the food after it has been subjected to the digestive 

 process. The vessels that are concerned in it are the lacteals, or 

 absorbents of the intestinal walls. These are engaged almost exclu- 



