CHAPTER V. 



SECRETION OF THE MUCOUS MEMBRANE. 



Mucus. 



ALL the internal parts of the animal body which are connected 

 by direct continuity with the external surface, are covered by 

 a soft velvety and highly vascular coat the mucous membrane, 

 which in its turn is protected by a delicate layer of epithelium. 1 



The mucous surfaces, especially when they are in a state of 

 irritation, secrete a viscid, stringy, and often tough fluid ; occa- 

 sionally it is clear and colourless, but most commonly it is 

 turbid, of a faint yellow or grayish white colour, and is frequently 

 of sufficient consistence to separate in gelatinous globular masses, 

 or tough flocculi. 



Of normal mucus. 



The transition from healthy to diseased mucus is so inde- 

 finitely characterized, that it is almost impossible to draw a 

 strict line of demarcation between them, and the same remark 

 is equally applicable to the further change of the diseased se- 

 cretion into pus : hence it is not very easy to form a distinct 

 conception of what normal mucus really is. 



Henle states that in the same manner as the outer surface of 

 the external skin is continually peeling off and giving place to 



1 According to Henle the epithelium consists of one or more layers of cells which, 

 from the peculiarity of their form, are arranged in three groups: 1st, Pavement 

 epithelium [the scaly epithelium of Bowman], fig. 14 a, which occurs in the mouth, 

 in the intestinal canal as far as the pylorus, in the vagina, &c. : 2d, Cylinder epithe- 

 lium, [the prismatic of Bowman, the columnar of Todd,] fig. 14 b, having a conical 

 form, and arranged perpendicularly to the basement membrane ; this form occurs in 

 the portion of the intestinal canal below the pylorus, in the gall-bladder, and in the 

 male genito-urinary apparatus : and 3d, The ciliated epithelium, fig. 14 c, which re- 

 sembles the cylinder epithelium in form, and has its free edges armed with cilia. 

 This occurs in the respiratory organs, in the uterus, and fallopian tubes. 



