178 



THE ESSENTIALS OF HISTOLOGY. 



a small artery which joins the capillary network at the base of the 

 villus ; the corresponding vein generally arises nearer the extremity. 



The lymphatics (lacteals) of the mucous membrane (fig. 209), after 

 receiving the central lacteals of the villi, pour their contents into a 

 plexus of large valved lymphatics which lie in the submucous tissue 

 and form sinuses around the bases of the lymphoid nodules. From 

 the submucous tissue efferent vessels pass through the muscular coat, 

 receiving the lymph from an intramuscular plexus of lymphatics, and 

 are conveyed away between the layers of the mesentery. 



FIG. 209. VERTICAL SECTION OF A PORTION OF A PATCH OF PETER'S GLANDS WITH 



THE LACTEAL VESSELS INJECTED. (32 diameters. ) (Frey. ) 



The specimen is from the lower part of the ileum : a, villi, with their lacteals left white ; 

 b, some of the tubular glands ; c, the muscular layer of the mucous membrane ; d, cupola 

 or projecting part of the nodule ; e, central part ; /, the reticulated lacteal vessels occu- 



the 



Absorption of fat. The lymph-corpuscles of the villi are in some 

 animals e.g. rat, frog important agents in effecting the passage of fat- 

 particles into the lacteals. In other animals much of the fat is absorbed 

 in the form of soap, and takes a fluid form in its passage into the lacteals 

 of the villi. In order to study the process of transference, it is con- 

 venient to stain the fat with osmic acid, which colours it black. It 

 can then be observed that in animals of the former category which 

 have been fed with fat these particles are present (1) in the columnar 

 epithelium-cells ; (2) in the lymph-cells ; and (3) in the central lacteal 

 of the villus. The lymph-cells are present not only in the reticular 

 tissue of the villus, but also in considerable number between the 

 epithelium-cells ; and they can also be seen in thin sections from osmic 

 preparation within the commencing lacteal ; but in the last situation 

 they are undergoing disintegration. 



