circus. 51 



These principles pass out of the cells upon the surface of the. 

 membrane in connection with water and inorganic salts in 

 variable proportion. Many of the cells themselves are des- 

 quamated, and are found in the secretion, together with a 

 few leucocytes, which are produced upon mucous surfaces 

 with great facility. 



Composition and Varieties of Mucus. In comparing 

 the secretions of the different mucous membranes, each one 

 will be found to possess certain distinctive peculiarities, more 

 or less marked ; but there are certain general characters 

 which belong to all varieties of mucus. The fluid is usually 

 a mixture of the secretion from the simple membrane and 

 the product of its follicles or glandular appendages, and al- 

 ways contains a certain amount of desquamated epithelium ; 

 and it is frequently possible, from the microscopical charac- 

 ters of the epithelium, to indicate the part by which any given 

 specimen of mucus was secreted. This desquamation of 

 epithelium must not be regarded as a necessary condition of 

 the secretion of mucus, any more than the desquamation of 

 the epidermic scales is to be regarded as a condition neces- 

 sary to the secretion of perspiration or sebaceous matter. It 

 is a property of the epidermis and the epithelial covering of 

 mucous membranes to be regenerated by the formation of 

 new cells from below, the effete structures being thrown off, 

 and the admixture of these with mucus is simply accidental. 

 The leucocytes, formerly called mucus-corpuscles, are the 

 result of irritation of the mucous membrane, and are not 

 constant constituents of normal mucus. 



All the varieties of mucus are more or less viscid ; but 

 this character is very variable in the secretions from differ- 

 ent membranes, in some of them the secretion being quite 

 fluid, and in others almost semisolid. 



The different kinds of mucus vary considerably in general 

 appearance. Some of them are perfectly clear and colorless ; 

 but the secretion is generally grayish and semitransparent. 



