extremity in a closed tube, while the other opens into a common duct.
The mucus varies in composition in different parts of the body; but in
all, it contains a small portion of insoluble animal matter. Its
functions are threefold. It lubricates the membranes, prevents their
injury, and facilitates the passage of food through the alimentary
canal.

SALIVA. This term is given to the first of the digestive fluids, which
is secreted in the glands of the mouth. It is a viscid, alkaline liquid,
with a specific gravity of about 1005. If allowed to stand, a whitish
precipitate is formed. Examinations with the microscope show it to be
composed of minute, granular cells and oil globules, mingled with
numerous scales of epithelium. According to Bidder and Schmidt, the
composition of saliva is as follows:

Water, 995.16
Organic matter, 1.34
Sulpho-cyanide of Potassium, 0.06
Phosphates of Sodium, Calcium and Magnesium, .98
Chlorides of Sodium and Potassium, .84
Mixture of Epithelium, 1.62
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1000.00

Two kinds of organic matter are present in the saliva; one, termed
_ptyalin_, imparts to the saliva its viscidity, and it obtained from the
secretions of the parotid, submaxillary and sublingual glands; another,
which is not glutinous, is distinguished by the property of coagulating
when subjected to heat. The saliva is composed of four elementary
secretions, derived respectively, from the mucous follicles of the