MUCUS. 507 



these cavities from the action of those foreign matters. It is dis- 

 tinguished by the name of the cavity in which it is secreted. 

 Thus we have the mucus of the mouth, of the nose, of the trachea; 

 of the stomach and intestines, of the gall-bladder, and of the uri- 

 nary organs. 



By mucus is meant in chemistry a solid body, which does not 

 dissolve in water ;'lbut which absorbs that liquid, swells up, be- 

 comes soft, viscid, and even half-fluid in some cases. It is se- 

 creted by small glands^ scattered over the mucous membranes, 

 which throw it out, and spread it equably over the whole surface 

 of the mucous membrane. It is soaked with water, holding 

 in solution^the same salts which exist in the serum of the 

 blood. 



Its characters vary somewhat in different mucous membranes, 

 doubtless according to the nature of the foreign substances from 

 which it is intended to protect the membrane on which it is spread. 

 On this^account it will be requisite to give the chemical proper- 

 ties of the different species of mucus so far as they have been 

 determined. 



1. Mucus of the mouth. This mucus subsides from saliva 

 left at rest in small white flocks. In sulphuric, muriatic, and 

 acetic acids, it becomes transparent and horny. But it does not 

 dissolve in these acids, nor give out any phosphate of lime to 

 them ; though when incinerated it always leaves traces of that 

 salt.* 



2. Mucus of the nose. This mucus, when secreted from a 

 healthy membrane, is white or colourless, translucent, loaded 

 with water, so as to assume much of the appearance of that por- 

 tion of gum-tragacanth which is insoluble in cold water after it 

 has imbibed as much as it can of that liquid. In the first stage 

 of a catarrh, it is secreted in greater abundance than usual, 

 and is at first transparent and almost altogether liquid ; but 

 as the disease advances the mucus acquires more and more 

 consistency, becomes white and opaque, and finally yellow 

 and nearly solid. Healthy mucus of the nose, according to the 

 analysis of Berzelius, is composed of the following constitu- 

 ents: 



* Berzelius. 



