31 PROGRESS OE VETERINARY SCIENCE AND ART. 
the study of physiology is but a series of inferences drawn 
from anatomy, how much easier is it to show that it is 
absurd to think that pathological investigations tend to en- 
lighten us on questions of physiology. This is the rarest 
exception ; and however loudly people may speak of physio- 
logical knowledge acquired by years of practical study of 
disease, the best proof that they have learned little is that 
they have produced little, and that they can claim no position 
amongst the cultivators of science. 
Bernard, in his lectures, first engages our attention by the 
salivary glands, the physiological properties of which, as he 
says, have been known to us but recently. 
In man and mammalia the structure of all salivary glands 
is very much alike. Such is the opinion of the most re- 
nowned histologists, and amongst them Kblliker. The ducts 
of these glands vary, but they must be considered as quite 
distinct from the glands themselves, so far as structure is 
concerned. The salivary glands of birds vary histologically 
from those of mammalia ; but the epithelium, which is cha- 
racteristic in a gland of this kind, is much the same in all. 
If anatomically no difference is noticed in the structure of 
these glands, each of them has, however, very distinct phy- 
siological properties in relation with peculiar functions. The 
glands of the mouth are separately or combinedly destined to 
co-operate in three sets of physiological phenomena, viz., 
taste > mastication , and deglutition . 
Parotid Gland. — The parotid gland has a very im- 
portant office to perform in the process of mastication, and 
it bears a constant relation with the extent and importance 
of the latter function. Its secretion is altogether peculiar, 
and is strangely modified by nervous influences. 
The parotidean saliva is not being constantly secreted, but 
more especially when the jaws are made to move. Its 
amount is in relation to the kind of food and the efforts 
required for its reduction. Mastication goes on slowly if 
the parotidean secretion be suppressed, and the loss of saliva 
by accidental fistulae, &c., induces a sensation of thirst. 
Thirst is not a local sensation, but the indication of a want 
of the economy for the reparation of its liquids. If horses with 
fistulae of the parotid structure be. made to drink, the secre- 
tion from the gland is arrested. This is not observed with 
the other salivary glands. 
Pure parotidean saliva does not contain any alkaline vis- 
cosity. When of the temperature of the body it is clear, but 
it becomes slightly opaline on cooling, in virtue of the pre- 
cipitation of a sub-salt. It becomes coated by a whitish 
