636 ABSORPTION. 



jected to the absorbing action of cells, by which their decomposition is 

 effected, and their elements conveyed into the blood; whilst antago- 

 nizing cells elaborate from the blood, and deposit fresh particles in the 

 place of those that 'have been removed. These various substances, 

 bone, muscle, hair, nail, as the case may be, are never found, in 

 their compound state, in the blood ; and the inference, consequently, is 

 that at the very radicles of the absorbents and exhalants, the sub- 

 stance on which absorption or exhalation has to be effected, is reduced 

 to its constituents, and this by an action, to which we know nothing 

 similar in physics or chemistry: hence, it has been inferred, that the 

 operation is one of the acts of vitality. 



All the various absorptions may be classed under two heads: the 

 external and the internal; the former including those that take place 

 on extraneous matters from the surface of the body or its prolongation 

 the mucous membranes; and the latter, those that are effected inter- 

 nally, on matters proceeding from the body itself, by the removal of 

 parts already deposited. By some physiologists, the action of the air 

 in respiration has been referred to the former of these ; and the whole 

 function of absorption has been defined; the aggregate of actions, by 

 which nutritive substances external and internal are converted into 

 fluids, which serve as the basis of arterial blood. The function of respi- 

 ration will be investigated separately. Our attention will, at pre- 

 sent, be directed to the other varieties; and, first of all to that which 

 occurs in the digestive tube. 



I. DIGESTIVE ABSORPTION. 



The absorption, effected in the organs of digestion, is of two kinds; 

 according as it concerns liquids of a certain degree of tenuity, or solids. 

 The former, it has been remarked, are subjected to no digestive action, 

 but disappear chiefly from the stomach, and in part from the small 

 intestine. The latter undergo conversion, before they are fitted to be 

 taken up from the intestinal canal. 



a. Absorption of Chyle or Ghylosis. 



1. ANATOMY OF THE CHYLIFEROUS APPARATUS. 



In the lower animals, absorption is effected over the whole surface of 

 the body, both as regards the materials necessary for nutrition and the 

 supply of air. No distinct organs for the performance of these func- 

 tions are perceptible. In the upper classes of animals, however, we 

 find an apparatus, manifestly intended for the absorption of chyle, and 

 constituting a vascular communication between the small intestine and 

 left subclavian. Along this channel, the chyle passes, to be emptied 

 into that venous trunk. 



The chyliferous apparatus consists of chyliferous vessels, mesenteric 

 glands, and thoracic duct. The chyliferous vessels or lacteals, arise 

 from the inner surface of the small intestine; in the villi, which are at 

 the surface of, and between, the valvulse conniventes. Prof. E. H. Weber 1 

 has, however, seen them distributed in the interspaces between the 



1 Mutter's Archiv., u. s. w., s. 400, Berlin, 1847. 



