NATURE OF THE SALIVA IN HORSE AND DOG. 165 
The same proceeding is applicable to most of the herbivorous 
animals. The rabbit, however, offers a totally different 
arrangement; the ductus Stenonis in this species presents 
the same relations as in the dog; it therefore becomes indis¬ 
pensable to operate as in the case of this latter animal. 
The parotidean duct in the dog passes through the muscular 
fibres of the masseter, and, following a direct course, opens 
into the mouth in front of the second molar. In order to 
practise the same operation as before, the lower edge of the 
zygomatic arch must be felt for, and followed from its pos¬ 
terior to its anterior extremity; a slight depression will thus 
be discovered ; at this very point the duct passes into the 
mouth. Let a horizontal incision be made over this point; 
the duct will be easily discovered ; but the facial vessels and 
nerve, which lie before it, must be previously dissected with 
care, and then drawn aside with a curved probe ; the duct 
immediately appears beneath them; nothing remains but to 
open it and plunge a tube within its cavity. 
(M. Bernard performs the experiment on a middle-sized 
dog. At the moment when the duct is laid open the animal 
utters a few plaintive cries. This proves, according to M. 
Bernard’s remark, that the parotidean duct is sometimes 
endowed with sensibility, although the reverse is usually 
the case.) 
You see, gentlemen, that not a single drop of saliva escapes 
at this moment from the tube; in general, the fluid is only 
secreted during the process of mastication and deglutition, or 
under the impression of acute pain or of a powerful sapid 
sensation. You are well aware that various moral influences 
are capable of exciting its secretion ; the fact is a well-known 
one in man, and can be equally verified in the lower animals. 
The horse which has just undergone the operation we have 
performed in your presence has been fasting for several 
hours; the mere sight of his food will immediately bring on 
an abundant secretion. 
(A bundle of hay being brought in, the animal exhibits 
great excitement, and a jet of saliva flows from the tube.) 
Acids, however, are of all the agents that can be brought 
to bear upon the salivary glands the most powerful. 
Berzelius has remarked, several years ago, that alkaline 
secretions were excited by acid substances, and vice versa; 
now, saliva, being an alkaline secretion, is likely to be elicited 
by the action of acids upon the gustative nerves, while alkalies 
remain comparatively inefficient. 
(The experiment is tried on the dog, into the parotid duct 
of which a tube had been previously introduced. A few 
