104 THE MICROSCOPIST. 



If any of the above tissues are to be kept, they should be 

 mounted in fluid, as spirit and water, or the creasote liquid. 



Mucous AND SEROUS MEMBRANE. Mucous membrane is 

 the investment of all the internal parts of the body, continu- 

 ous with the skin. Every cavity, organ, or gland, which 

 opens on the surface, is lined by it. Shut sacs are lined by 

 serous membrane. 



These membranes may be divided into two parts : the 

 epithelium, and the basement membrane. The external skin 

 is evidently a similar structure, somewhat modified, and is 

 capable, under certain circumstances, of taking on a similar 

 function. The epithelium of skin is the cuticle or epidermis, 

 but the basement membrane, though present, is not easily 

 shown, except where the surface is raised into papillae. 



The epithelium exists in three varieties : the scaly, prismatic, 

 and spheroidal. * The first kind is most largely developed in 

 the skin'; the cuticle, with its horns, hairs, hoofs, and feathers, 

 &c., is made up of it. Detached scales may be obtained from 

 the inner side of the mouth or by scraping any of the serous 

 membranes gently with a knife. The prismatic ; or according 

 to Dr. Todd, the columnar ; is abundant throughout the stomach 

 and intestines, and even the lungs. Each prism is attached by 

 its sides to its fellows, and endwise to the basement membrane. 

 The attached extremity is generally pointed, the free one wide 

 and flat, and covered with vibratile cilia, which may be often 

 observed in rapid motion, some time after the death of the 

 animal. The third variety, or spheroidal, is to be met with in 

 all glandular structures, as the tubes of the stomach and kidney, 

 and the secreting structure of the liver. 



The basement membrane is structureless, and is not supplied 

 in any way with vessels. The best places for viewing it are 

 the tubes of the kidney and stomach, and the villi of the small 

 intestine. It is supported upon a submucous areolar tissue, in 



