PTYALIN. 329 
of extracting the salivary glands with glycerin, precipitating the 
glycerin extract with excess of alcohol, washing with strong alcohol, 
and then extracting with water. 
Effects of reaction. — A knowledge of the effects of change of 
reaction on the amylolytic activity of ptyalin, apart from its intrinsic 
interest, possesses considerable importance from the bearing it has on 
the natural process of digestion of starch, and for this reason probably 
the subject has attracted the attention of a great number of workers. 1 
Ptyalin is secreted in an alkaline fluid, the saliva, and after a few 
seconds admixture with the food passes with it into the stomach ; here 
its alkaline reaction is lessened by the gastric secretion, and finally 
replaced by an acid reaction. The amount of starch changed by the 
ptyalin will depend on the effect of this gradual diminution in alkalinity 
on its activity, and if the activity is decreased thereby, on the rate at 
which progress is made towards an acid reaction. 
It was formerly supposed that ptyalin was only active in a fluid 
of alkaline reaction, that it was in consequence only active during 
the few seconds of mastication, while the food remained in the 
mouth, and was instantly destroyed on coming in contact with 
gastric juice. More recent observations have, however, shown that 
the importance of saliva as a digestive fluid is much underrated by 
such a view. 
The diastatic action of ptyalin attains a maximum when the reaction 
of the fluid containing it is neutral, or even faintly acid, provided the 
acidity is due to acid combined with proteid. Even mere traces oifree 
acid, however, lessen and rapidly destroy its activity. Sodium carbonate 
added to neutralised saliva decreases its activity, and in greater 
quantity arrests it ; here, again, proteids present in solution play a 
protecting part, and by combining with the alkali prevent its injurious 
action on the ferment. A solution of ptyalin free of proteid would 
therefore probably act best in a neutral fluid, and would be quickly 
destroyed by either an acid or alkaline reaction, due to acid or alkali 
uncombined with proteid. 2 
The diastatic action of the saliva, therefore, continues in the stomach 
during and after a meal until (1) the alkali of the saliva has been 
neutralised, (2) the proteid present in solution has been satisfied, and 
(3) a trace of free hydrochloric acid remains in excess. According 
1 Jacubowitsch, Lehmann's " Zoochemie," in Gmelin's " Haudbuch der Chem.," 
Heidelberg, 1858, Bd. viii. S. 22 ; Paschutin, Arch. f. Anat. u. Physiol. , Leipzig, 1871, 
S. 366 ; Hammarsten, Jahresb. u. d. Fortschr. d. Thier-Chcm., Wiesbaden, 1871, Bd. i. 
S. 35 ; Briicke, Sitzungsb. d. k. Akad. d. Wissensch., Wien, 1872, Abtli. 3 ; Watson, 
Trans. Chem. Soc, London, 1879, p. 539 ; Chittenden and Grisvvold, Am. Chem. Journ., 
Baltimore, 1881, vol. iii. p. 305 ; Falk, Jahresb. ii. d. Fortschr. d. Thier-Chem., Wiesbaden, 
1881, Bd. xi. S. 444 ; Langley, Journ. Physiol., Cambridge and London, 1880-2, vol. iii. 
p. 246 ; Nylen, Jahresb. ii. d. Fortschr. d. Thier-Chem., Wiesbaden, 1882, Bd. xii. S. 
241 ; Chittenden and Ely, Am. Chem. Journ., Baltimore, 1882, vol. iv. ; Journ. Physiol., 
Cambridge and London, 1882, vol. iii. p. 327 ; Detmar, Ztschr. f. physiol. Chem., 
Strassburg, 1882, Bd. vii. S. 1 ; Langley and Eves, Journ. Physiol., Cambridge and 
London, 1883, vol. iv. p. 18 ; Chittenden and Smith, Chem. News, London, 1885, vol. 
liii. : Stud. Lab. Physiol. Chem., New Haven, 1885, vol. i. p. 1 ; John, Centralbl. f. klin. 
Med., Bonn, Bd. xii.; Schlesinger, Virchoic's Archiv, 1891, Bd. cxxv. S. 146 ; Schierbach, 
Skandin. Arch. f. Physiol., Leipzig, 1892, Bd. iii. S. 344; Ebstein u. Sehulze, Virchoic's 
Archiv, 1893, Bd. cxxxiv. S. 475. 
2 It is generally held that ptyalin acts best in neutral solution or with a faint acid 
reaction, due to acid combined with proteid ; but there are slight differences of opinion as to 
where the exact optimum point lies, for which the original papers should be consulted, 
especially those by Langley and by Chittenden and their co-workers. 
