454 DIGESTION. 



tation of the glandular nerves, either directly (in animals), or reflexly, 

 by mechanical or chemical irritation of the muccus membrane of the 

 mouth. Among the chemical irritants the acids take first place. Mas- 

 tication also exercises a strong influence upon the secretion of parotid 

 saliva, which is specially marked in certain herbivora. 



Human parotid saliva may be readily collected by the introduction 

 of a canula into STENSON'S duct. This saliva is thin, less alkaline than 

 the submaxillary saliva (the first drops are sometimes neutral or acid), 

 without special odor or taste. It contains a little protein but no mucin, 

 which is to be expected from the construction of the gland. It also con- 

 tains a diastatic enzyme, which, however, is absent in many animals. 

 The quantity of solids varies between 5 and 16 p. m. The specific gravity 

 is 1.003-1.012. Potassium sulphocyanide seems to be present, though 

 it is not a constant constituent. KULZ 1 found a maximum of 1.46 per 

 cent oxygen, 3.8 per cent nitrogen, and in all 66.7 per cent carbon dioxide 

 in human parotid saliva. The quantity of firmly combined carbon dioxide 

 was 62 per cent. 



The quantity and composition of the saliva, from the mucin glands 

 as well as from the albuminous glands, show differences in the various 

 classes of animals but these cannot be entered into here. According 

 to PAWLOW 2 and his pupils the quantity as well as the composition of 

 the saliva of the various glands and the mixed saliva in dogs is to a great 

 degree dependent upon the psychical stimulation, but also upon the 

 kind of substances introduced into the mouth, and an adaptation of 

 the glands for various mechanical and chemical irritants is found to occur. 



POPIELSKI 3 disputes the existence of such an accommodation (in 

 dogs) to the kind of food and to the kind of stimulation. In man an 

 accommodation of the salivary glands, to the needs, has also been sug- 

 gested but the statements are still .not unanimous. 1 See also Chapter 

 I (page 53). 



The mixed buccal saliva in man is a colorless, faintly opalescent, 

 slightly ropy, easily frothing liquid without special odor or taste. It 

 is made turbid by epithelium cells, mucous and salivary corpuscles, 

 and often by food residues. Like the submaxillary and parotid saliva, 

 on exposure to the air it becomes covered with an incrustation consist- 

 ing of calcium carbonate and a small quantity of an organic substance, 



1 Zeitschr. f . Biologie, 23. 



2 Arch, internal, de Physiol., 1, 1904. See also Boos, Maly's Jahresber., 36. 390, 

 and Neilson and Terry. Amer. Journ. of Physiol., 15, as well as the work of Mendel 

 and Underbill, Journ. of biol. Chem., 3. 



"Popielski, Pfluger's Arch., 127; Zebrowski, Pfluger's Arch., 110; Neilson and 

 Lewis, Journ. of biol. Chem., 4, with Scheele, ibid., 5; Carlson and Chittenden, Amer. 

 Journ. of Physiol., 20. 



