STOMACH AND INTESTINE. 



355 



which immediately succeeds death. And their 

 duration is rarely protracted beyond a few 

 minutes. 



Changes in the villi during digestion. Dur- 

 ing the act of digestion, the villi undergo cer- 

 tain noticeable alterations. At this period, 

 they receive an increased afflux of blood ; 

 and become both larger and softer. They ac- 

 quire a greater opacity ; so as to appear whiter 

 by reflected, and darker by transmitted, light. 

 The nuclei and cells which occupy their in- 

 terior are greatly increased in number and dis- 

 tinctness. And, finally, after the ingestion of 

 food containing the usual fatty ingredients, 

 a portion of these may be found occupying 

 the interior of the villi themselves. 



The process by which fatty matter pene- 

 trates the villus to enter the lacteal in its 

 centre, deserves our special attention, from 

 the fact that it constitutes the origin of the 

 chyle. At present we shall limit ourselves 

 to a description of the appearances actually 

 observed, in connection with the mucous 

 membrane of the alimentary canal. 



The first step towards the absorption of 

 the fatty matter, consists in its entry into the 

 epithelium which invests the exterior of the 

 villus. Each columnar cell of this covering 

 is gradually filled by a large oil globule ; which 

 occupies the whole of its cavity, with the ex- 

 ception of that small portion devoted to its 

 nucleus. This change first implicates a few 

 scattered epithelia ; and, by rendering them 



Fig. 265. 



VWus of the dog about two hours after feeding : show- 

 ing the entry of fatty into scattered epithelia on its 

 surface. Magnified about 400 diameters. 



a, a, outline of the villus formed by epithelia with 

 their ordinary contents; b, b, epithelia rendered 

 bright and refractile by their fatty contents. 



more refractile, often causes various parts of 

 the surface of the villus to offer a curious con- 

 trast of bright spots (b,fig. 265.) and darker 



intervals.* Gradually, however, all the cells 

 become similarly affected ; so that the entire 

 vilius assumes the altered appearance just 

 alluded to. 



The next step towards the absorption of the 

 fatty matter consists in the minute subdivi- 

 sion of the single oil globule (c^Jig. 266.) 

 which occupies the epithelial cell. The way 

 in which this process occurs is unknown : 



Fig. 266. 



Isolated epithelial cells from a villus^ as seen during the 

 absorption of fat into the lacteals. (Altered from 

 KoeUiker.") Magnified 350 diameters. 



a, columnar epithelial cell, occupied by fatty 

 molecules; b, similar cell, containing several small 

 oil-drops; c, similar cell, enclosing a single oil- 

 drop ; rf, similar cell completely filled by a larger 

 oil -drop. The upper or free end of the cell (at d) 

 js concave. 



but the result of the change is to give the 

 columnar cell a darkly granular appearance 

 (#, Jig 266.), in which we may often distin- 

 guish separate, though minute, fatty mole- 

 cules. These molecules are next found in 

 the substance of the villus itself, though 

 chiefly towards its surface and free extre- 

 mity ; to the apex of which latter part 

 they are often limited.-f- From the sub- 

 stance or matrix of the villus, the molecules 

 of fat are then transferred to the lacteal trunk 

 occupying its centre ; which, in the most fa- 

 vourable instances, they define as a slender 

 column of dark fatty granules. 



How far the above process constitutes a 

 mere act of physical imbibition, it is difficult 

 at present to determine. But that it is so, at 

 least in part, can scarcely be doubted. For the 

 experiments of Matteucci J (which are con- 

 firmed in all their essential particulars by 

 Valentin ) prove that, when a dilute alkaline 

 solution and a faintly alkaline fatty emulsion 

 are separated from each other by an animal 

 membrane, diffusion occurs between them. 

 And the circumstances actually present in 

 the intestine are even more favourable to 

 such a transit than those which obtained 

 in the experiments of these observers. The 

 lymph and blood are sometimes more alkaline 

 than the solution which they made use of. 

 The degree in which the tenuity of the delicate 

 cell-wail of the villus exceeds that of the 



* These appearances, alluded to by Frerichs ( Op. 

 cit. p. 854.) and detailed by Koelliker (Op. cit. p. 

 167.), were noticed by me eight years ago in the 

 human subject. 



f The larger drops sometimes seen in this situation 

 are, I believe, the result of accidental violence to 

 the specimen. 



t Le9ons sur les Phenomenes, &c., pp. 104, 5. 



Op. cit. vol. i. p. 379. 



A A 2 



