

DIGESTION. 



matters aid in giving to the masticated food the requisite consistency, 

 and also serve to lubricate its surface and facilitate deglutition. This 

 is evident from the fact that the principal trouble resulting from defi- 

 ciency of the saliva is a difficulty in the mechanical processes of masti- 

 cation and swallowing. Food which is hard and dry, like crusts or 

 crackers, cannot be masticated and swallowed with readiness, unless 

 properly moistened. If the saliva be excluded from the mouth, its loss 

 does not interfere so much with the chemical changes of the food in 

 digestion, as with its physical preparation. This is the result of exper- 

 iments performed by various observers. Bidder and Schmidt,* after 

 tying Steno's duct, together with the common duct of the submaxillary 

 and sublingual glands on both sides in the dog, found that the imme- 

 diate effect of such an operation was "a remarkable diminution of the 

 fluids exuding 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 the air. Deglutition was 

 therefore rendered difficult not only for dry food, like bread, but even 

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

 mals also became very thirsty, and were constantly ready to drink.' 7 



Bernardf also found that the only marked effect of cutting off the 

 flow of saliva was a difficulty in mastication and deglutition. He first 

 administered to a horse 500 grammes of oats, and found that this quan- 

 tity was masticated and swallowed in 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 ; each mouthful, as it 

 passed down the oesophagus, being received at the opening and exam- 

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

 was then divided, and another similar quantity of oats given to the 

 animal. Mastication and deglutition were at once retarded. The 

 alimentary masses passed down the oesophagus at longer intervals, 

 and their interior was no longer moist and pasty, but dry and brittle. 

 Finally, at the end of twenty-five minutes, the animal had succeeded 

 in masticating and swallowing only about three-quarters of the quan- 

 tity which he had previously disposed of in nine minutes. 



It appears, furthermore, from the experiments of Magendie, Ber- 

 nard, and Lassaigne, on horses and cows, that the quantity of saliva 

 absorbed by food during mastication is in direct proportion to its 

 hardness and dryness, but has no particular relation to its chemical 

 qualities. These experiments were performed as follows : The oesoph- 

 agus was opened at the lower part of the neck, and tied between the 

 wound and the stomach. The animal was then supplied with a pre- 

 viously weighed quantity of food, and this, as it passed out by the 

 oesophageal opening, was collected and again weighed. The differ- 

 ence in its weight, before and after swallowing, indicated the quantity 



* Verdauungssaefte und Stoffwechsel, p. 3. 



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



