518 SPECIAL HISTOLOGY. 



by cell membranes, elements -whicli are perhaps never entirely absent 

 in a villus, but are at other times far fewer, and particularly are not to 

 be distinguished in its interior.* 



§ 154. Crlands of the small intestine. — The small intestine contains 

 only two kinds of true glands ; viz., 1, tubular glands, which are dis- 



the channels between the mucous and submucous membrane. If the villi be much dis- 

 tended, a portion of the chyle passes back again through the epithelial cells into the cavity 

 of the intestinal tube, and this is especially apt to occur when the chyle contains any par- 

 ticles too coarse to circulate. The chyle is propelled further by the muscular con- 

 tractions of the intestines into the vessels of the mesentery, whence it is pumped, as it 

 were, into the thoracic duct, by the alternating pressure on the intestinal walls during the 

 movements of resj^iration. This action is also aided to a slight extent by the contractions 

 of the muscular tissue of the chyliferous vessels. 



The results arrived at by Professor Brilcke, will, if corroborated by future research, tend 

 greatly to elucidate much that has hitherto been obscure in the physiology of the digestive 

 as well as of interstitial absorption. — DaC] 



* [One of the most important contributions to our knowledge of the anatomy of the villi 

 and the general physiology of digestive absorption, which has appeared for a long time, is 

 Professor Briich's '-Beitrage zur Anatomic und Physiologie der Donndarm-Schleimhaut," 

 in Siebold and KoUiker's " Zeitschrift," for April, 1S53. We subjoin the principal results 

 at which the Professor has arrived. 



The epitlielium is not cast off during normal digestion and in freshly killed animals it is 

 somewhat difhcult to detach it from the mucous membrane. The cells of the epithelium 

 do not, as Weber stated, undergo any change of form during digestion andchylification, but 

 they become filled with fat, wliich gradually passes on into the villi, &c., so that in the 

 fasting state they are again free from any foreign contents. 



The villi ordinarily contain two, but sometimes many, capillary trvmks, which ramify 

 principally at their apices, and superficially. Ramifications and anastomoses in the body of 

 the villi are less common. In dogs, many parallel vessels often run undivided for a con- 

 siderable distance, and have doubtless been confounded with a central lacteal. 



In all the animals Briicli examined, and in man, he found that the villi had a striking 

 uniformity of structure. A single lacteal ran, without dividing, through the villus, and terminated 

 shortly befo7-e reaching its apex, in a cacal commonly enlarged fjirf (Liberkiihn's ampulla). The 

 lacteal had no wall, appearing to be a mere excavation in the villus. In cleft villi, the 

 lacteal was cleft, each end terminating in a caecum. In very rare cases, there were in 

 broad villi two lacteals, a shorter and a longer, terminating in distinct ampulla, side by side. 

 In tlie mucous membrane itself, the lacteals form a wide superficial network. 



BrQcli accounts for the supposed lacteal network of the villi, by showing that the blood- 

 vessels are as capable of absorbing fat as the lacteals, and when filled, of course acquire the ap- 

 pearance of a lacteal network. In some cases he found the superficial capillary network of 

 a villus half red and half white, and it was frequently possible, when the fatty contents of 

 the capillary network were hidden by the preponderating blood, to render them obvious by 

 the action of water, which dissolved out the coloring matter and thus apparently converted 

 a capillary, into a lacteal network. 



Professor Briich considers that the absorption of fit is a purely mechanical process, "just 

 as quicksilver is pressed through leather," and he doubts altogether that the lacteals have 

 any special absorbent fimction, or differ from ordinary lymphatics. However, we think 

 that the mechanical nature of the process is open to very great question, and we should 

 rather compare the manner in which fat enters a villus, to that in which the ingesta enter 

 nn .Sclinophrys ; one can as readily comprehend the existence of a selective power in the 

 former as in the latter case. That some such faculty exists would seem to be indicated by 

 the fact stated by Bruch, that the Liebcrkuhnian and Peyerian glands take no share in fatty 

 absorption ; though, on the ether hand, it must be remembered that Kolliker found the eggs 

 of Entozoa in the villi of rabbits (" Mikr. Anat.," B. II. 2, 173).— Trs.] 



