ABSORPTION. 303 



of experiments, the quantity of lymph traversing the thoracic duct of a 

 dog in twenty-four hours was found to be about equal to two-thirds of 

 the blood in the body. (Bidder and Schmidt.) 



Absorption by the Lacteals. During the passage of the chyme 

 along the whole tract of the intestinal canal, its completely digested parts 

 are absorbed by the blood-vessels and lacteals distributed in the mucous 

 membrane. The blood-vessels appear to absorb chiefly the dissolved por- 

 tions of the food, and these, including especially the albuminous and sac- 

 charine, they imbibe without choice; whatever can mix with the blood 

 passes into the vessels, as will be presently described. But the lacteals 

 appear to absorb only certain constituents of the food, including par- 

 ticularly the fatty portions. The absorption by both sets of vessels is 

 carried on most actively but not exclusively, in the villi of the small in* 

 tcstine; for in these minute processes, both the capillary blood-vessels and 

 the lacteals are brought almost into contact with the intestinal contents. 

 There seems to be no doubt that absorption of fatty matters during diges- 

 tion, from the contents of the intestines, is effected chiefly between the 

 epithelial cells which line the intestinal tract (Watney), and especially 

 those which clothe the surface of the villi. Thence, the fatty particles 

 are passed on into the interior of the lacteal vessels (Fig. 216, a), but 

 how they pass, and what laws govern their so doing, are not at present 

 exactly known. 



The process of absorption is assisted by the pressure exercised on the 

 contents of the intestines by their contractile walls; and the absorption of 

 fatty particles is also facilitated by the presence of the bile, and the pan- 

 creatic and intestinal secretions, which moisten the absorbing surface. 

 For it has been found by experiment, that the passage of oil through an 

 animal membrane is made much easier when the latter is impregnated 

 with an alkaline fluid. 



Absorption by the Lymphatics. The real source of the lymph, 

 and the mode in which its absorption is effected by the lymphatic vessels, 

 were long matters of discussion. But the problem has been much sim- 

 plified by more accurate knowledge of the anatomical relations of the 

 lymphatic capillaries. The lymph is, without doubt, identical in great 

 part with the liquor sanguinis, which, as before remarked, is always 

 exuding from the blood-capillaries into the interstices of the tissues in 

 which they lie; and as these interstices form in most parts of the body 

 the beginnings of the lymphatics, the source of the lymph is sufficiently 

 obvious. In connection with this may be mentioned the fact that changes 

 in the character of the lymph correspond very closely with changes in the 

 character of either the whole mass of blood, or of that in the vessels of 

 the part from which the lymph is exuded. Thus it appears that the 

 coagulability of the lymph is directly proportionate to that of the blood; 

 and that when fluids are injected into the blood-vessels in sufficient qnan- 



