THE SALIVA. 151 



if any, had been produced by transformation of the starch. Colin 1 

 has found the farinaceous matter of oats and of starchy roots recogniz- 

 able by its iodine reaction, after these substances had remained in the 

 first stomach of the ox, mixed with saliva, for twenty-four hours. The 

 same observer introduced into the interior of the paunch, through a 

 fistula, small muslin bags containing uncooked potato starch, which 

 were found in the same cavity, still full of unaltered starch, at the end 

 of twenty and twenty-two hours. It is worth remembering furthermore 

 that the salivary glands and their secretion are also abundantly devel- 

 oped in the carnivora, whose food never in the natural condition con- 

 tains starch as an ingredient. 



It appears evident, therefore, that the chemical action of the saliva in 

 the lower animals forms no part of the natural process of digestion ; 

 and that in man it is insignificant in amount, and quite subordinate to 

 that of other digestive fluids. In both animals and man, however, and 

 in the carnivora as well as in the herbivora, its physical properties are 

 important in accomplishing the processes of mastication and degluti- 

 tion. 



Mastication is aided and controlled in great measure by the sen- 

 sibilities of touch and taste, residing in the surface of the tongue and 

 other parts of the mucous membrane. The sense of taste notifies us 

 of the alimentary qualities of the food taken into the mouth, and 

 its sapid qualities must be fully brought out by the comminution and 

 moistening of the food before mastication is complete. The taste itself 

 depends, for one of its essential conditions, upon a sufficient supply of 

 saliva, and this is by no means an unimportant function of the secretion. 

 No substance can produce an impression upon the nerves of taste unless 

 it be in a fluid form and capable of absorption by the mucous membrane. 

 The saliva produces this effect upon the soluble ingredients of the food, 

 and brings them in contact with the papillae of the tongue in sufficient 

 quantity to produce a gustatory sensation. 



The general sensibility of the tongue, which is highly developed, 

 also enables this organ to appreciate the physical condition of the food 

 and how far it is prepared for deglutition. At the same time its mus- 

 cular apparatus provides for its movement in every direction. When 

 the alimentary material is finally reduced, by mastication and mixture 

 with the saliva, to a sufficiently pasty and homogeneous condition, the 

 softened mass is collected from every part of the mouth by the move- 

 ments of the tongue and brought together upon its upper surface. It 

 is then pressed backward by the muscular force of the organ, and car- 

 ried through the fauces into the pharynx and upper part of the oesopha- 

 gus. Here it passes beyond the control of the will. It is then grasped 

 by the muscular fibres of the oesophagus, and by the continuous and rapid 

 peristaltic action of this canal is carried downward into the stomach. 



1 Physiologic compare des Animaux Domestiques. Paris, 1854, tome i. p. 603. 



