132 DIGESTION. 



retarded. The alimentary masses passed down the oesophagus at 

 longer intervals, and their interior was no longer moist and pasty, 

 as before, 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 quantity which he had previously 

 disposed of in nine minutes. 



It appears also, from the experiments of Magendie, Bernard, and 

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

 by the food during mastication is in direct proportion to its hard- 

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

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

 phagus was opened at the lower part of the neck, and a ligature 

 placed upon it, between the wound and the stomach. The animal 

 was then supplied with a previously weighed quantity of food, and 

 this, as it passed out by the cesophageal opening, was received into 

 appropriate vessels and again weighed. The difference in weight, 

 before and after swallowing, indicated the quantity of saliva absorbed 

 by the food. The following table gives the results of some of Las- 

 saigne's experiments, 1 performed upon a horse : 



KIND OF FOOD EMPLOYED. QUANTITY OF SALIVA ABSORBED. 



For 100 parts of hay there were absorbed 400 parts saliva. 



" barley meal " 186 " 



" oats " 113 " 



" green stalks and leaves- " 49 " 



It is evident from the above facts, that the quantity of saliva 

 produced has not so much to do with the chemical character of the 

 food as with its physical condition. When the food is dry and 

 hard, and requires much mastication, the saliva is secreted in 

 abundance ; when it is soft and moist, a smaller quantity of the 

 secretion is poured out ; and finally, when the food is taken in a 

 fluid form, as soup or milk, or reduced to powder and moistened 

 artificially with a very large quantity of water, it is not mixed at 

 all with the saliva, but passes at once into the cavity of the stomach. 

 The abundant and watery fluid of the parotid gland is most useful 

 in assisting mastication ; while the glairy and mucous secretion of 

 the submaxillary gland and the muciparous follicles serve to lubri- 

 cate the exterior of the triturated mass, and facilitate its passage 

 through the oesophagus. 



By the combined operation of the two processes which the food 

 undergoes in the cavity of the mouth, its preliminary preparation 



1 Comptes Rendus, vol. xxi. p. 362. 



