356 SECRETION. 



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

 is generally grayish and semitransparent. Examined by the microscope, in addition to 

 the mixture of epithelium and the occasional leucocytes, which give to the fluid its semi- 

 opaque character, the mass of the secretion presents a very finely-striated appearance, as 

 though it were composed of thin layers of a nearly transparent substance, with many 

 folds. These delicate striae do not usually interlace with each other, and they are ren- 

 dered more distinct by the action of acetic acid. This appearance, with the peculiar 

 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 coagu- 

 lated 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 exceedingly diificult to get an exact idea of the proximate composition of nor- 

 mal 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, how- 

 ever, contain a peculiar organic principle, called mucosine, which gives to the fluid its 

 peculiar viscidity. They likewise present a considerable variety of inorganic salts, as the 

 chlorides of sodium and potassium, alkaline lactates, carbonate of soda, phosphate of 

 lime, a small proportion of the sulphates, and, in some varieties, traces of iron and silica. 

 Of all these constituents, mucosine is the most important, as it gives to the secretion its 

 characteristic properties. Like all other organic nitrogenized principles, mucosine is 

 coagulable by various reagents. It is imperfectly coagulated by heat ; and, after desica- 

 tion, 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 alco- 

 hol, forming a fibrinous clot soluble in hot and cold water. Mucosine 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 been dried, be exposed to water, 

 it assumes the viscid consistence peculiar to mncosine. This property serves to distin- 

 guish it from albumen and other organic nitrogenized principles. 



Nasal Mucus. The nasal mucus, being subject to so many changes from irritation of 

 the Schneiderian membrane, presents considerable variation in its appearance and com- 

 position. Under perfectly normal conditions, it is very viscid, clear or slightly opaque 

 and grayish, and strongly alkaline. It always contains more or less columnar epithelium. 

 In its behavior in the presence of various reagents, it presents the characteristics which 

 we have ascribed to the secretions of the mucous membranes generally. The following 

 is the composition of the normal secretion : 



Composition of JVasal Mucus. (Robin.) 



Water 933*00 to 947'00 



Mucosine (with a trace of albumen ?) 63*30 " 54'80 



Lactate of soda (?) : 1-00 " 5'00 



Organic crystalline principles 2'00 " 1'05 



Fatty matters and cholesterine not estimated. 5 '01 



Chlorides of sodium and potassium 5-60 to 5'09 



Calcareous and alkaline phosphates 3-50 " 2*00 



Sulphate and carbonate of soda 0'90 not estimated. 



Bronchial and Pulmonary Mucus. This is the secretion of the general mucous sur- 

 face of the larynx and bronchial tubes, mixed with the products of the glands situated in 

 the substance of these membranes and in the submucous tissue. In addition to this 

 secretion, there is an exhalation of watery vapor containing traces of organic matter, com- 



