116 INSALIVATION. 



The saliva undergoes material change in disease, and be- 

 comes acid, being likewise charged with an excess of organic 

 principles. It may contain urea and various other adventi- 

 tious principles. 



The uses of the saliva are various. In the first place it 

 acts mechanically in softening the 'food. This is one reason 

 why vegetable feeders require more than carnivora. It faci- 

 litates the trituration of food, and combines, with the pha- 

 ryngeal liquids hereafter to be described, in enabling the 

 bolus to pass through the oesophagus. 



The saliva, in virtue of the large proportion of water it 

 contains, is a solvent for all soluble materials such as sugar, 

 salts, &c., which the food contains. 



But the saliva is destined for another purpose which is 

 totally unconnected with the act of mastication, and which it 

 serves, especially in ruminants, by being swallowed and re- 

 tained in compartments of the stomach in contact with food. 

 This action consists in the transformation of starchy matter? 

 into dextrine or gum, and into sugar. This change does not 

 occur with any of the secretions taken separately outside the 

 body; and, according to Bernard, even if the various salivas 

 are separately obtained from the principal glands and mixed, 

 the starchy principles are not acted upon. The buccal glands 

 seem to exert a special function in connection with the pro- 

 duction of a chemically active saliva, and this depends pro- 

 bably on the tendency to decomposition, the change being 

 favoured by all causes which favour chemical changes. 

 Many other organic substances induce such a transformation 

 of starchy principles, and in some animals the digestion of 

 amylaceous principles by the saliva, seems to be a very un- 

 important office. The acid of the stomach stops its action, 

 and, as we shall afterwards see, it is in the large intestine of 

 the horse that the change referred to in amylaceous matters 



