WITH THE MICROSCOPE. 131 



229. Examination of Mucous Membrane. Mucous membrane 

 consists of one or more layers of epithelium, which rest upon a 

 transparent texture. This surface tissue gradually passes into 

 areolar tissue (sub-mucous arcolar tissue, sub-basement tissue or corium). 

 Into this structure, muscular fibres, or their tendons, when these 

 exist, are inserted. In it ramify the vessels and nerves. The thick- 

 ness of the mucous membrane and other characters of the several 

 structures of which it is composed vary much in different localities. 

 The mucous membrane of the mouth, especially at the back part of 

 the tongue, may be readily subjected to examination, and the dif- 

 ferent structures enumerated may be made out. It is desirable to 

 inject the vessels with a transparent injection, and cut thin sections 

 through the mucous membrane and subjacent structures with a sharp 

 knife. The basement membrane is very easily demonstrated in the 

 tube of the kidney. On the anatomy of mucous membrane, the 

 reader is strongly recommended to consult Mr. Bowman's article 

 " Mucous Membrane," in the Cyclopaedia of Anatomy and Phy- 

 siology. 



Examination of Organs of Digestion and Absorption. 



23O. Epithelium. Sub-mucous Areoiar Tissue. The epithe- 

 lium of mucous membranes is very readily subjected to exami- 

 nation, and its character is found to vary much according to 

 the locality from which it is taken. In order to obtain a specimen 

 of epithelium from a mucous membrane, all that is required i-s to 

 scrape gently the surface of the tongue or inside of the cheek with a 

 knife, and place what has been removed upon a glass slide, and, 

 after moistening it with a little water, syrup, or a mixture of glycerine 

 and water, which does not cause the cells to become so turgid from 

 osmosis, the specimen may be placed in the microscope. This 

 epithelium approximates in its characters to that of which the 

 epidermis or cuticle is composed. The cells obtained are almost all 

 of them mature and some are very old, invaded by fungi and about 

 to be cast off, pi. XXXII, fig. 203. The thin glass cover should not 

 be allowed to press too strongly upon the specimen. This may be 

 prevented by inserting one or two pieces of hair or thin hog's bristles. 

 The epithelium upon the surface of the tongue of the frog, toad, 

 newt, and that lining the mouth of the serpent and some other 

 reptiles is ciliated. See fig. 236, pi. XXXVII, also p. 161. 



In many of the glands which may be regarded as cavities open- 

 ing upon the surface of the mucous membrane and continuous with 



K 2 



