510 OF ABSORPTION AND SANGUIFICATION. 



Fig. 204. several smaller branches, whose origin it is difficult to 



trace ; but it is probable that they form loops by anasto- 

 mosis with each other, so that there is no proper free 

 extremity in any case. It is quite certain that the lac- 

 teals never open by free orifices upon the surface of the 

 intestine, as was formerly imagined. From the researches 

 of Mr. J. Goodsir, already referred to ( 181), it appears 

 that these loops are imbedded in a mass of cells, which 

 are the real agents in the selection of the materials that 

 are destined to be conveyed into the lacteals. When 



these cells have distended themselves, by their inherent 



power of growth, with the materials which are adapted 



One of the intestinal vilLi. r . ' . . , . . r . 



with the commencement of to their selecting function, and have reached their full 

 a lacteal. term of maturity, they appear to yield their contents to 



the absorbent vessels, either by bursting or by deli- 

 quescence. It is thought by Prof. E. Weber, that the epithelial cells, which 

 cover the villus, perform a preliminary office; the nutrient matter being first 

 absorbed and partially prepared by them ; and then being drawn, through the 

 basement membrane of the villus, into the special absorbent cells which form 

 part of its substance. This seems the more likely, as we shall hereafter 

 find that the epithelial cells of the placental tufts appear to perform a like 

 function. 



673. The mill are also furnished with a minute plexus of blood-vessels ; 

 of which the larger branches may be seen with the naked eye, when they are 

 distended with blood, or with coloured injection (Figs. 205, 206). The par- 

 ticular arrangement of the capillaries of which the plexus is formed, varies in 

 different animals; but in all they seem to be most copiously distributed upon 

 the surface of the villus. The purpose of these may be partly to afford some 

 of the materials for the development of the absorbent cells ; and this would 

 seem probable from the recent experiments of Mr. Fenwick,* which show 

 that the lacteals will not absorb alimentary matter from any part of the intes- 

 tinal canal, in which the blood is not circulating. But there can be no reason- 

 able doubt, that the blood-vessels of the mucous membrane lining the digestive 

 cavity, and especially those of the villi, perform an important part in the func- 

 tion of Absorption. This is established by the fact, that soluble substances 

 introduced into the stomach, and prevented from passing beyond its pyloric 

 orifice, are absorbed from its walls. 



674. In regard to the degree ia which the function of Nutritive Absorp- 

 tion is performed by the Lacteals, and by the Sanguiferous System, respect- 

 ively, considerable difference of opinion has prevailed. When the Absorbent 

 vessels were first discovered, and their functional importance perceived, it 

 was imagined that the introduction of alimentary fluid into the vascular sys- 

 tem took place by them alone. A slight knowledge of Comparative Anatomy, 

 however, might have sufficed to correct this error; since no lacteals exist in 

 the Invertebrated animals, the function of Absorption being performed by the 

 Mesenteric, blood-vessels only ; from which it is evident, that these do pos- 

 sess the power of absorption : and it is scarcely to be supposed that they 

 should not exercise this power in Vertebrated animals also, since their dis- 

 position on the walls of the intestinal cavity is evidently favourable to it. On 

 the other hand, the introduction of a new and distinct system of vessels would 

 seem to indicate, that they must have some special purpose ; and there can 

 be no doubt that the absorption of certain kinds of nutritive matter is that 

 for which they are peculiarly designed. The fluid found in the lacteals is 



* Lancet. Jan. and Feb. 1845. 



