SALIVA. 131 



therefore, of saliva on starch, though a curious and interesting pro- 

 perty, has no significance as to its physiological function, since it 

 does not take place in the natural digestive process. We shall see 

 hereafter that there are other means provided for the digestion of 

 starchy matters, altogether independent of the action of the saliva. 



The true function of the saliva is altogether a physical one. Its 

 action is simply to moisten the food and facilitate its mastication, 

 as well as to lubricate the triturated mass, and assist its passage 

 down the oesophagus. Food which is hard and dry, like crusts, 

 crackers, &c., cannot be masticated and swallowed with readiness, 

 unless moistened by some fluid. If the saliva, therefore, be prevented 

 from entering the cavity of the mouth, its loss does not interfere 

 directly with the chemical changes of the food in digestion, but only 

 with its mechanical preparation. This is the result of direct experi- 

 ments performed by various observers. Bidder and Schmidt, 1 after 

 tying Steno's duct, together with the common duct of the sub- 

 maxillary and sublingual glands on both sides in the dog, found 

 that the immediate effect of such an operation was " a remarkable 

 diminution of the fluids which exude upon the surfaces of the mouth ; 

 so that these surfaces retained their natural moisture only so long 

 as the mouth was closed, and readily became dry on exposure to 

 contact with the air. Accordingly, deglutition became evidently 

 difficult and laborious, not only for dry food, like bread, but even 

 for that of a tolerably moist consistency, like fresh meat. The 

 animals also became very thirsty, and were constantly ready to 

 drink." 



Bernard 3 also found that the only marked effect of cutting off 

 the flow of saliva from the mouth was a difficulty in the mechani- 

 cal processes of mastication and deglutition. He first administered 

 to a horse one pound of oats, in order to ascertain the rapidity with 

 which mastication would naturally be accomplished. The above 

 quantity of grain was thoroughly masticated and swallowed at the 

 end of nine minutes. An opening had been previously made in 

 the oesophagus at the lower part of the neck, so that none of the 

 food reached the stomach ; but each mouthful, as it passed down the 

 oesophagus, was received at the cesophageal opening and examined 

 by the experimenter. The parotid duct on each side of the face 

 was then divided, and another pound of oats given to the animal. 

 Mastication and deglutition were both found to be immediately 



1 Op. cit., p. 3. 



2 Lemons de Physiologic Experimentale, Paris, 1856, p. 146. 



