22 THE SECRETION OF PAROTID SALIVA. [BOOK II. 



the degree of activity of these muscles. Thus if cannulse be tied into 

 the Stenonian ducts of a ruminant, it will be observed that during 

 mastication of the food, which in these animals is effected alternately 

 by the molars of the two sides of the jaws, the flow of parotid saliva 

 alternates likewise, being always more abundant on the side on which 

 the muscles of mastication are more active. Again, if the amount of 

 parotid saliva flowing from a parotid fistula be observed in the case of 

 a horse which is fed first upon dry aliments such as oats, requiring 

 powerful efforts of mastication, and then upon soft watery food such 

 as bran mash, the amount of the salivary fluid secreted in the first 

 case will be very much greater than in the second. 



These facts, which we derive from the researches of Claude 

 Bernard, establish clearly enough the peculiarly close relationship 

 which exists between the parotid secretion and the mechanical 

 movements of mastication, a relationship the existence of which is 

 also borne out by the fact that the parotid is relatively more highly 

 developed in animals, such as ruminants, in which the process of 

 mastication is most perfectly performed, and less developed in 

 animals, like carnivores, in which the food is swallowed in large 

 masses. In intimate agreement with the part which it has to play 

 in moistening the aliments which are to be subjected to the process 

 of mastication, we find the parotid saliva to be less viscid and more 

 watery than the secretion of the other salivary glands. 



The nerves The nerve fibres which influence the secretion of 



which influ- parotid saliva are derived (a) from the sympathetic, 

 ence the paro- (ft) from the glosso-pharyngeal nerve, though the course 

 e lon * which the latter pursue is one peculiarly devious, 

 viz. through its tympanic branch or nerve of Jacobson, to the 

 small superficial petrosal, thence to the otic ganglion 1 , and from 

 it into the auriculo-temporal nerve, of which branches pass into the 

 parotid gland. According to the view of Heidenhain, the secretory 

 fibres, i.e. those which influence the quantity of the secretion by par- 

 ticularly influencing the amount of water which the gland separates 

 from the blood, are derived from the glosso-pharyngeal, whilst the 

 trophic, which directly influence the metabolism of the secretory cells, 

 are contained in the sympathetic filaments distributed to the gland. 



A stimulation of Jacobson's nerve causes in the dog an abundant 

 flow of watery saliva ; a stimulation of the sympathetic does not 

 apparently in the dog occasion any secretion, but it increases very 

 notably the amount of solid matter contained in the secretion which 

 flows on simultaneous stimulation of Jacobson's nerve. In the cat 



1 Doubts long prevailed as to the source of the secretory fibres which reach the 

 parotid through the otic ganglion. The opinion long prevailed that these were derived 

 through the small superficial petrosal n. from the 7th, but the careful experiments of 

 Eckhard and Heidenhain have shewn that whilst intracranial stimulation of the 7th is 

 never followed by a flow of parotid saliva, this result is always obtained when Jacob- 

 son's nerve is stimulated. We must therefore perforce abandon the seductive theory 

 that the 7th nerve supplies the secretory filaments to all the salivary glands, and admit 

 that the mainly sensory glosso-pharyngeal shares these functions. 



