FUNCTIONS OF THE SALIVA. 175 



cation of experiments made on an exclusively carnivorous ani- 

 mal, like the dog, to the digestive process in man. While there 

 is no reason to suppose that there is any material difference 

 in the mammalia, as regards the general operation of some 

 of the functions, such as circulation or respiration, it is evi- 

 dent that differences exist in the properties of the digestive 

 fluids, as well as in the teeth and jaws, corresponding with 

 the great differences in the character and conditions of the 

 alimentary principles. In the study of digestion, therefore, 

 the results of experiments on the inferior animals cannot 

 always be taken without reserve, and must be confirmed by 

 observations on the human subject; but fortunately, the 

 properties of nearly all of the digestive fluids which have 

 been studied minutely by vivisections have been investigated 

 more or less fully in man. 



In 1831, Leuchs discovered that hydrated starch, mixed 

 with fresh saliva and warmed, became liquid in the space of 

 several hours and was converted into sugar. 1 This fact has 

 since been repeatedly confirmed ; and it is now a matter of 

 common observation that hydrated starch, or unleavened 

 bread, taken into the mouth, almost instantly loses the prop- 

 erty of striking a blue color with iodine, and responds to the 

 usual tests for sugar. Of the rapidity of this action any one 

 can easily convince himself by the simple experiment of tak- 

 ing a little cooked starch into the mouth, mixing it well with 

 the saliva, and testing in the ordinary way for sugar. This 

 can hardly be done so rapidly that the reaction is not mani- 

 fested ; and the presence of sugar is also indicated by the taste. 

 Though the human mixed saliva will finally exert the same 

 action on uncooked starch, the transformation takes place 

 much more slowly. It has been shown by experiment that all 

 the varieties of human saliva have the same effect on starch 

 as the mixed fluids of the mouth. Dalton found no difference 

 in the pure parotid saliva and the mixed saliva of the human 

 subject as regards the power of transforming starch into su- 



1 BURDACH, Traite de Physiologic, Paris, 1841, tome ix., p. 265. 



