160 DIGESTION. 



estimated ; but Prof. Dalton found that during mastication, 

 the quantity secreted in twenty minutes on one side was 

 127*5 grains, and on the other side, 374 '4 grains. 



A curious fact with regard to the influence of mastica- 

 tion upon the flow from the parotids was observed by Colin 

 in the horse, ass, and ox. He found that when mastication 

 was performed on one side of the mouth, the flow from the 

 gland on that side was greatly increased, exceeding by sev- 

 eral times the quantity produced on the opposite side. 1 This 

 fact was confirmed by Dalton, as already indicated, in the 

 human subject. 2 



The flow of saliva from the parotid takes place with 

 greatly increased activity during the process of mastication. 

 The orifice of the parotid duct is so situated that the fluid 

 is poured directly upon the mass of food as it is undergoing 

 trituration by the teeth ; and as the secretion is more abun- 

 dant on the side on which mastication is going on, and as 

 the consistence of the fluid is such as to enable it to mix 

 readily with the food, the function of this gland is supposed 

 to be particularly connected with mastication. This is un- 

 doubtedly the fact ; though its flow is not absolutely confined 

 to the period of mastication, but continues, in small quantity, 

 in the intervals. Its quantity is regulated somewhat by the 

 character of the food, being much greater when the articles 

 taken into the mouth are dry than when they contain consid- 

 erable moisture. Colin has shown in some of the herbivora 

 a remarkable insensibility of the parotids to the stimulus of 

 sapid and aromatic substances applied to the mucous mem- 

 brane of the cheeks. In the ruminants, in which there is a 

 constant flow from these glands, the quantity cannot be in- 

 creased by the action of salts, feeble acids, or aromatic sub- 

 stances. 3 The experiments of Bernard on dogs show a cer- 



1 COLIN, Traite de PJiysiologie Comparee des Animaux Domestiques, Paris, 

 1854, tome i., p. 468. 

 3 Loc. cit. 

 8 Op. cit., p. 471. 



