84 ABSOKPTION. 



able material may, under certain conditions, be exposed to arterial blood 

 without oxidation. Yet that this want of action is wholly due to inci- 

 dental circumstances is shown from the fact that salts of organic acids 

 are much more quickly oxidized in the blood than they are in the open 

 air. 



It is interesting thus to observe how the death of one part of the body 

 Advanta e mm i sters to the life of the rest ; for the nitrogenized and act- 

 taken 'of the ive principles of t!^ juices secreted for the accomplishment of 

 portion toor- digestion are on the descending career, and are truly dying 

 ganize an- matter. The incipient stage of decay through which they are 

 passing reacts on the food, and prepares it in a temporary 

 manner to replace those parts of the body which are ceasing from activ- 

 ity, and about to be removed. 



CHAPTER V. 



OF ABSORPTION. 



Double Mechanism for Absorption. The Lacteals and Veins. Lacteal Absorption. Descrip- 

 tion of a Villus. Analogies in Plants. Introduction of Fat by the Villi. The Chyle. 

 Causes of the Flow of Chyle. Intermediate Changes on its Passage to the Blood. Action of 

 Peyer's Bodies. Lymphatic Absorption. Nature of Lymph. Structure of the Lymphatic 

 System. Comparison of Chyle, Lymph, and Serum. Function of the Lymphatic System. 

 Production of Fibrin. Cutaneous Absorption. Causes of the Flow of Lymph. Apparent se- 

 lecting power of the Absorbents. Connection of the Lacteals and Lymphatics with the Locomo- 

 tive and Respiratory Mechanism. 



THE food, after digestion, though in the alimentary tract, is exterior to 

 Double mech- ^ e anniia l system. Means have therefore to be resorted to 

 anism for ab- for its introduction into the circulation, and its distribution 

 to every part. This is accomplished by a double mechanism, 

 one portion of which is adapted to the digestion which has been going on 

 in the stomach, the other to that which is completed in the intestine. 

 The veins which are profusely spread on the walls of the digestive cav- 

 ity constitute the former apparatus, the lacteal vessels the latter. 



The lacteal vessels may be described as delicate tubes, conveying ma- 

 Description of terials absorbed from the intestine into the blood. Their 

 a villas. mode of origin may be understood by considering them as 



projecting with a fine but blunt end upon the inner coat of the intestine. 

 This projection is covered over with smooth muscle cells and a plexus of 

 blood-vessels, a continuation, as it were, of those of the mucous coat of 

 the intestine itself; they are held together by connective tissue, and over 

 that is cast a covering of cylindric epithelium. This construction con- 



