CHAPTER XLV 

 DIGESTION IN THE MOUTH 



The Saliva. The saliva is secreted from three pairs of glands in 

 the region of the mouth. These are the parotid, the submaxillary, 

 and the sublingual. It is also secreted by other minute glands con- 

 tained in the buccal mucous membrane. The character of the saliva 

 varies in the different glands. 



The parotid of man and most animals yields a thin serous (albumin- 

 ous) saliva, while from the submaxillary gland " mixed " saliva, partly 

 serous or watery, partly mucous or viscid, is usually obtained; in the 

 rabbit, however, the secretion of the submaxillary glands is wholly 

 serous. Saliva is a mixture of the secretions of all these glands. 

 The parotid saliva of man is a thin, faintly alkaline fluid, containing 

 but little protein and no mucus. Its specific gravity varies from 

 1003 to 1012. It contains a starch-splitting enzyme ptyalin and 

 in most cases a small amount of potassium sulphocyanide, with a 

 variable small amount of salts (0-5 to 1-6 per cent.) and gases in solu- 

 tion (oxygen, nitrogen, and carbon dioxide). The oxygen in the saliv a 

 is greater in amount than that which is dissolved in water when exposed 

 to the atmosphere. The excess must be secreted in the saliva. 



SubmaxiDary saliva varies according to the exciting conditions. 

 In man, the submaxillary saliva is ordinarily a clear, viscid, alkaline 

 secretion, with a specific gravity of 1002 to 1005, and about 0-3 to 

 0-5 per cent, of solids. It contains much mucin, traces of protein 

 and the ferment ptyalin, potassium sulphocyanide, and inorganic 

 salts, the chief of which are the chlorides of sodium and potassium, 

 the phosphates of calcium and magnesium, and the bicarbonate of 

 calcium and sodium. Traces of sulphates are also present. In 

 the dog two kinds of submaxillary saliva are recognized: that pro- 

 duced by stimulation of the chorda tympani nerve, known as 

 chorda saliva, and that produced by stimulation of the sympathetic 

 nerve, known as sympathetic saliva. Chorda saliva is the abundant 

 secretion of the gland, having a specific gravity of 1003 to 1005, and 

 containing about 1-2 to 14 per cent, of solids. Sympathetic saliva is 

 very much smaller in amount, and considerably richer in solids 

 (1-6 to 2-8 per cent.). Its specific gravity is 1007 to 1018. 



Sublingual saliva, the most alkaline of the salivas, is transparent, 

 viscid saliva, comparatively rich in mucin and solids. It also contains 

 ptyalin and potassium sulphocyanide. 



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