COMPOSITION AND VARIETIES OF MUCUS. 319 



tion of mucus in addition to what has already been stated in connection with 

 the general mechanism of secretion. All the mucous membranes are quite 

 vascular, and the cells covering the membrane and lining the follicles and 

 glands attached to it have the property of taking from the blood the materi- 

 als necessary for the formation of the secretion. These matters pass out of 

 the cells upon the surface of the membrane, in connection with water and 

 inorganic salts in variable proportions. Many of the cells themselves are 

 thrown off and are found in the secretion, together with a few leucocytes, 

 which latter are produced upon mucous surfaces with great facility. 



Composition and Varieties of 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 semi-solid. The different kinds of mucus vary considerably in gen- 

 eral appearance. Some of them are perfectly clear and colorless ; but the 

 secretion is generally grayish and semi-transparent. Examined by the mi- 

 croscope, in addition to the mixture of epithelium and the occasional leuco- 

 cytes, which give to the fluid its semi-opaque character, the mass of the secre- 

 tion presents a very finely striated appearance, as though it were composed 

 of thin layers of nearly transparent substance with many folds. These deli- 

 cate strife do not usually interlace with each other, and they are rendered 

 more distinct by the action of acetic acid. This appearance, with the pecul- 

 iar effect of the acid, is characteristic of mucus. Some varieties of mucus 

 present very fine, pale granulations and a few small globules of oil. 



On the addition of water, mucus is somewhat swollen but is not dissolved. 

 An exception to this is the secretion of the conjunctival mucous membrane, 

 which is coagulated on the addition of water. As a rule the reaction of 

 mucus is alkaline ; the only exception to this being the vaginal mucus, 

 which is very fluid and is distinctly acid. 



It is difficult to get an exact idea of the composition of normal mucus, 

 from the fact that the quantity secreted by the membranes in their natural 

 condition is very small, being just sufficient to lubricate their surface. All 

 varieties, however, contain a peculiar organic matter, called mucine, which 

 gives to the fluid its peculiar viscidity. They likewise present a consid- 

 erable variety of inorganic salts, as sodium chloride, potassium, chloride, 

 alkaline lactates, sodium carbonate, calcium phosphate, a small propor- 

 tion of the sulphates, and in some varieties, traces of iron and of silica. Of 

 all these constituents, mucine is the most important, as it gives to the 

 secretion its characteristic properties. Like all other organic nitrogenized 

 substances, mucine is coagulable by various reagents. It is imperfectly coag- 

 ulated by heat ; and after desiccation it can be made to assume its peculiar 

 consistence by the addition of a small quantity of water. It is coagulated 

 by acetic acid and by a small quantity of the strong mineral acids, being 

 redissolved in an excess of the latter. It is also coagulated by strong alcohol, 

 forming a fibrinous clot soluble in hot and cold water. Mucine may be 

 readily isolated by adding water to a specimen of normal mucus, filtering, 

 and precipitating with an excess of alcohol. If this precipitate, after having 



