THE MUCOUS MEMBRANE. 137 



called villi from their velvety appearance, or their resem- 

 blance to the down of an unripe peach. 



Each villus consists of blood vessels, nerves and absorb- 

 ents bound together by cellular tissue, and not only cov- 

 ered by epithelium, but also, it is said, by an additional fine 

 membrane. These villi give origin to the lacteals by fine 

 branches, which, it is now found, do not have open orifices 

 upon their surface as formerly believed, but between the 

 capillary vessels at the extremity of each villus, while 

 chylous absorption is going on, are seen cells containing 

 an opalescent fluid. These cells disappear almost entirely, 

 it is said, when the chyle has left the intestine; the lac- 

 teals empty themselves, and the villi become flaccid. 



These cells are regarded as the special agents for select- 

 ing the nutrient matter and handing it over to the lacteals ; 

 they have a short life, and are constantly being renewed. 

 Another element of mucous membrane is found in the 

 follicles and glands scattered throughout its whole extent. 



The simple follicles of Leiberkuhn exist in immense 

 numbers every where upon the mucous surface. They con- 

 sist simply of depressions of the mucous surface, forming 

 small pouches, whose orifices are not visible to the naked 

 eye, but which are found to have eight or ten times the 

 diameter of the red globules of blood. 



Professor Homer has estimated the number of these fol- 

 licles to be about 25,000 to the square inch, and between 

 forty and fifty millions to the whole alimentary canal. 

 Their use is to supply the principal part of the mucous 

 fluid. The glands are simply compound cryptce or folli- 

 cles, having different forms and names, in different parts of 

 the mucous membrane. 



At the mouth of the Eustachian tube, the simple follicles 

 are collected in a body of somewhat oval form and almond 

 size, called the tonsil. In the oesophagus these follicles are 

 situated in the sub-mucous tissue, and lobulated, communi- 

 cating with the surface by a long excretory duct. 



In the stomach the glands are seen in the shape of long 

 tubes, situated perpendicularly, side by side, and, at their 



