166 
NATURE OF THE SALIVA IN HORSE AND DOG. 
drops of vinegar being poured into the mouth, saliva flows 
from the tube drop by drop; an alkaline solution being then 
substituted, no sensible result is obtained.) 
Let us now examine the saliva we have obtained from both 
animals. In the dog, as you see, it is a limpid and colourless 
fluid, the reaction of which is strongly alkaline. But this is 
not alwa 5 '^s the case. We find in Tiedemann and Gmelin’s 
great work on the digestive fluids that, after dividing the 
parotidean duct in a dog, they plunged its extremity into a 
small glass case, so as to obtain ten grammes (180 grains) of 
a viscous fluid, strongly resembling albumen in its general 
appearance. Such are, therefore, the properties which these 
celebrated observers acknowledge as characterising the paro¬ 
tidean secretion—a conclusion widely different from that 
W'hich we have just arrived at; and, in repeating the experi¬ 
ment on ten or twelve different animals, you would probably 
meet once or twice with the same result. How' is this 
apparent contradiction to be explained ? A peculiar anatomical 
distribution is its real cause. It sometimes occurs that, before 
opening into the mouth, the ductus Stenonis receives the 
excretory canals of tw'o or three little mucous glands, which 
impart the properties of their own secretion to the parotidean 
fluid. Nothing is easier than to prove this. In the animals 
w’hich offer this peculiarity let the duct be laid open above 
the point where it is joined by these tributary canals, and 
the normal and unmixed secretion of the gland will be ascer¬ 
tained to be exactly similar to that which we have just 
exhibited to you. In man the anatomical peculiarity we 
have noticed as an anomalous exception in the dog is normal. 
The parotidean saliva, as poured into the mouth, always, 
therefore, enjoys a certain degree of viscosity in our own 
species. In this respect we find the dog approaching closer 
to our ow’n organization than other animals. 
As to the saliva obtained from the horse, you see it offers, 
on the contrary, a viscid appearance; as in the dog, its 
reaction is strongly alkaline; but the action of heat, or the 
addition of nitric acid, precipitates an albuminous substance, 
W’hich appears to be peculiar to the equine genus, although 
its chemical composition has not yet been precisely ascertained. 
Let us now’ consider a few" of the more important charac¬ 
teristics of the secretion itself, viewed apart from the nature 
of the fluid produced. 
A tube being introduced into the parotidean duct in a 
living animal, it may be easily ascertained that the saliva only 
flows at intervals. In the horse, which during mastication 
emits prodigious quantities of it, the secretion now’ and then 
