98 SPECIAL HISTOLOGY. 



to the imbibition of an emulsive flud, such as milk, by a porous 

 body; and I believe that the fatty molecules of the chyme 

 are absorbed simply in consequence of their being carried along 

 with its fluid part. 



While digestion is going on, we frequently find the whole 

 parenchyma of the villi densely filled with small nuclei, here 

 and there surrounded by cell membranes, elements which 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. 1 ] 



1 [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 ' Beitriige zur Anatomie und Physiologie der Dunn- 

 darm-Schleimhaut,'in Siebold and Kblliker's 'Zeitschrift,' for April, 1853. We sub- 

 join the principal results at which the Professor has arrived. 



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

 it is somewhat difficult to detach it from the mucous membrane. The cells of the 

 epithelium do not, as Weber stated, undergo any change of form during digestion and 

 chylification, but they become filled with fat, which 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 trunks, 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 considerable distance, and have doubtless been confounded with a central 

 lacteal. 



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

 a striking uniformity of structure. A single lacteal ran, without dividing, through the 

 villus, and terminated shortly before reaching its apex, in a ccecal commonly enlarged 

 end (Lieberkiihn'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 ampidla, side by side. In the mucous membrane itself, 

 the lacteals form a wide superficial network. 



Briich 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 appearance 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 colour- 

 ing matter and thus apparently converted a capillary, into a lacteal network. 



Professor Briich considers that the absorption of fat is a purely mechanical process, 

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

 lacteals have any special absorbent function, 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 



