DIGESTION. 161 



fibers of nerves (preganglionic fibers) coming direct from the medulla 

 oblongata and spinal cord. 



The Parotid Saliva. The parotid saliva, as it flows from the 

 orifice of Stensen's duct, is clear, limpid, free from viscidity, dis- 

 tinctly alkaline in reaction, with a specific gravity of 1.003. Chemic 

 analysis shows that it consists of water, a small quantity of proteid 

 matter, a trace of a sulphocyanogen compound, and inorganic salts. * 

 The secretion is increased during mastication, and especially on the 

 side engaged in mastication. Dry food causes a larger flow than 

 moist food. The situation of the orifice of the parotid duct is such 

 that as the secretion is poured into the mouth it is at once incorporated 

 with the food by the movements of the lower jaw, and thus fulfils the 

 physical function of softening and moistening it. 



The Submaxillary Saliva. The submaxillary saliva is clear, 

 slightly viscid, alkaline in reaction, and has a specific gravity of 

 1.002. It consists of water, proteid matter (mucin), and inorganic 

 salts. 



The Sublingual Saliva. The sublingual saliva is clear, extremely 

 viscid, and strongly alkaline in reaction. It consists of water, proteid 

 matter (chiefly mucin), and inorganic salts. 



s The small racemose glands embedded in the mucous membrane 

 /on the inner surface of the cheeks and lips, on the hard and soft 

 / palate, on the tongue and pharynx, secrete a fluid which is grayish 

 I in color, extremely viscid and ropy. It contains a large amount of 

 1 mucin. 



Mixed Saliva. The saliva of the mouth is a complex fluid com- 

 posed of the secretions of all the salivary glands. As obtained from 

 the mouth it is frothy, colorless, slightly turbid, and somewhat viscid. 

 The specific gravity is low, ranging from 1.003 ta.i.oo6. The re- 

 action is usually distinctly alkaline. It may, however, be neutral 

 or even acid in reaction if there is any fermentation of food particles 

 in the mouth or as a result of disorders of the alimentary canal. 

 When examined with the microscope, the saliva is seen to contain 

 epithelial cells, salivary corpuscles resembling leukocytes, particles 

 of food, various microorganisms, and especially Leptothrix buccalis. 

 The chemic composition of the saliva is shown in the following 

 table: 



COMPOSITION OF HUMAN SALIVA. 



Water, 995-i6 994.20 



Epithelium, 1.62 2.20 



Soluble organic matter, 1.34 1.40 * 



Potassium sulphocyanid, 0.06 0.04 



Inorganic salts, 1.82 2.20 



1000.00 1000.04 



(Jacubowitsch.) (Hammerbacher.) 



II 



