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456 DIGESTION.
Ptyalin, or salivary diastase, is the amylolytic enzyme of the saliva.
This enzyme is found in human saliva, 1
but not in that of all animals,
especially not in the typical carnivora. It occurs not only in adults,
but also in new-born infants. In opposition to Zweifel’s views, Ber-
ger 2
claims that it is present not only in the parotid gland of children,
but also in the mucin glands.
According to H. Goldschmidt 3
the saliva (parotid saliva) of the horse does
not contain ptyalin, but a zymogen of the same, while in other animals and man
the ptyalin is formed from the zymogen during secretion. In horses the zymogen
is transformed into ptyalin during mastication, and bacteria seem to give the
impulse to this change. During precipitation with alcohol the zymogen is changed
into ptyalin.
Ptyalin has not been isolated in a pure form up to the present time.
It can be obtained purest by Cohnheim’s 4
method, which consists in
carrying the enzyme down mechanically with a calcium-phosphate
precipitate, and washing the precipitate with water, which dissolves the
ptyalin, and from which it can be obtained by precipitating with alcohol.
For the study or demonstration of the action of ptyalin one employs a
watery or glycerin extract of the salivary glands, or simply the saliva
itself.
Ptyalin, like other enzymes, is characterized by its action. This
consists in converting starch into dextrins and sugar. Our knowledge
as to the process going on here is just as uncertain as our knowledge
on the formation of sugar from starch (see page 229). The nature of
the sugar thus produced is known with certainty. For a long time it
was considered that glucose was the sugar formed from starch and
glycogen, but Seegen and O. Nasse have shown that this is not true.
Muculus and v. Mering have shown that the sugar formed by the
action of saliva, amylopsin, and diastase upon starch and glycogen is
for the most part maltose. This has been substantiated by Brown
and Heron. E. Kulz and J. Vogel 5
have also demonstrated that
in the saccharification of starch and glycogen, isomaltose, maltose, and
some glucose are formed, the varying quantities depending upon the
amount of ferment and the length of its action. The formation of
1
In regard to the variation in the quantity of ptyalin in human saliva see Hof-
bauer, Centralbl. f. Physiol., 10, and Chittenden and Richards, Amer. Journ. of Physiol.,
1; Schiile, Maly’s Jahresber., 29; Tezner, 1. c.
2
Zweifel, Untersuchungen iiber den Verdauungsapparat der Neugeborenen (Berlin,
1874); Berger, see Maly’s Jahresber., 30, 399.
1
Zeitschr. f. physiol. Chem., 10.
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