DIGESTION. 14:5 



food. Colin,* in experimenting upon the horse and the ox, also found 

 the parotid saliva excited by the movements of mastication, while the 

 submaxillary secretion was increased by introducing into the mouth 

 substances having a marked taste. Both the parotid and submaxillary 

 secretions are abundant while the animal is feeding, their quantity 

 being proportional to the rapidity of mastication and the sapid quality 

 of the alimentary substances. They are both either suspended or much 

 diminished during abstinence. In the ruminants, the sublingual saliva, 

 like the submaxillary, is excited by sapid substances and while the 

 animal is feeding. Its secretion continues during abstinence, contrib- 

 uting to keep the surfaces in a moist condition. 



Another indication of the different nervous influences by which the 

 salivary glands are controlled, is that in the ruminant animals, while 

 feeding, both the parotid and submaxillary glands furnish an abundant 

 supply of saliva ; but during rumination, although the parotid glands 

 are in full secretion, discharging frequently as much as 900 grammes 

 in fifteen minutes, the submaxillary glands are nearly or quite inac- 

 tive. Colin has also found that in the ox, horse, and ass, the parotid 

 glands of the two opposite sides, during mastication, are never in 

 active secretion at the same time ; but that they alternate with each 

 other, one remaining quiescent while the other is active. In these 

 - mastication is said to be unilateral; that is, when the animal 

 begins feeding or ruminating, the food is triturated for fifteen minutes 

 or more by the molars of one side only. It is then changed to the 

 opposite side, where mastication is performed for the succeeding fifteen 

 minutes. It is then changed back again, and so on alternately ; the 

 direction of the lateral movements of the jaw being frequently reversed 

 during the course of a meal. By establishing a salivary fistula simul- 

 taneously on each side, it is found that the flow of saliva corresponds 

 with the direction of the masticatory movement. When the animal 

 masticates on the right side, it is the right parotid which secretes 

 actively, while but little is supplied by the left ; when mastication is on 

 the left side, the left parotid pours out an abundance of fluid, while the 

 right is nearly inactive. 



We have observed a similar alternation in the human subject, when 

 mastication is changed from side to side. In an experiment of this 

 kind, the canula being inserted into the parotid duct of the left side, 

 the quantity of saliva discharged during twenty minutes, while masti- 

 cation was performed mainly on the opposite side of the mouth, was 

 8.26 grammes ; while the quantity during the same period, mastication 

 being on the same side of the mouth, was 24.25 grammes. It was 

 therefore nearly three times as much in the latter case as in the former. 



Daily Quantity of the Saliva. Owing to variations in the rapidity 

 of secretion of the saliva, and also to the fact that it is not excited in 

 the same way by artificial stimulus as by the presence of food, it is 



* Physiologie compares des Animaux Domestiques. Paris, 1854, tome i., p. 468. 



K 



