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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 * 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, internat. 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., 2(J.
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