DEPURATION. 429 
salivary glands saliva; and so on. But, as we shall hereafter find, there 
are minute points of difference in the arrangement of these cells in the 
different glands. It is now ascertained that the elements of the various 
secretions exist in the blood; and therefore the office of the glands is 
confined to the selection and separation of their products, and they have 
little or nothing to do with their conversion. 
DEPURATION, AND ITS OFFICE IN THE ANIMAL 
ECONOMY. 
THE WHOLE OF THE VARIOUS SECRETIONS which go on in the body are 
necessary for the due preservation of its health ; but the most important 
of the class alluded to above as excretions, must be removed from the 
blood, or death will speedily ensue. Thus, if saliva and gastric juice, as 
well as the other secretions aiding digestion, are not mixed with the food, 
the nutrition of the body will be imperfectly carried on, and its health 
will suffer. But if the elements of bile and urine are retained in the 
blood, not only is the system upset, but absolute death is produced in 
severe cases. Hence it follows, that attention to the state of the organs of 
depuration, or excretion, is of more importance even than to those of 
secretion, using these terms in the sense explained in the last paragraph. 
The chief organs of depuration are the lungs, which remove carbon from 
the blood ; the liver, which secretes the bile ; the kidneys, which get rid 
of the urea ; and the skin, which relieves it of its superfluous watery and 
some small proportion of its solid particles. Experiment shows that the 
retention of carbon, or urea, in the blood is speedily followed by death ; 
while the non-secretion of bile, if entire, poisons the system; and in 
milder cases, its absence from the alimentary canal interferes with the due 
elaboration of the chyle. 
ANATOMY OF THE SALIVARY GLANDS, PHARYNX, 
CESOPHAGUS, AND STOMACH. 
THE SALIVARY GLANDS are grouped around the jaw, three on each side, 
and are named the parotid, submaxillary, and sublingual glands. 
THE PAROTID (so named from its proximity to the ear, zapa, near ; ovs, 
aros, the ear) is the largest of the three, and lies in the space between the 
ramus of the lower jaw and the petrous part of the temporal bone, covered 
by the parotido-auricularis muscle (see muscles, fig. 2-16). It is enveloped 
in a case of dense cellular membrane, being itself made up of a number 
of little lobes, each of which has an investment continuous with the 
external one. The lobes have each an excretory duct, and these unite 
together like the stalks of a grape to form one single duct, which passes 
along the inner part of the angle of the jaw, along the border of the 
masseter, piercing the mucous membrane of the mouth opposite the second 
molar tooth. THE SUBMAXILLARY GLAND les within and before the angle 
of the jaw, and is of the same structure as the parotid. Its duct passes 
forward by the side of the root of the tongue, and opens on the side of 
the frenum. THE SUBLINGUAL GLAND is the smallest of the three, and is 
situated between the middle of the tongue and the lower jaw. Its ducts, 
which are several in number, open on the side of the freenum of the tongue, 
. close to the orifice of the submaxillary gland. Tuer sativa secreted by 
these glands contains various saline and earthy matters identical with those 
of the blood, and a peculiar substance called ptyalie, which is the ferment 
