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 " Handbuch 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-Chem., Wiesbaden, 1871, Bd. i. 

 S. 35; Briicke, Sitzungsb. d. Tc. Akad. d. Wissensch., Wien, 1872, Abth. 3; Watson, 

 Trans. Chem. Soc., London, 1879, p. 539 ; Chittenden and Grisvvold, Am. Chem. Journ., 

 Baltimore, 1881, vol. iii. p. 305 ; Falk, Jahresb. U. d. Fortschr. d. Thicr-Chem., Wiesbaden, 

 1881, Bd. xi. S. 444 ; Langley, Journ. Physiol., Cambridge and London, 1880-2, vol. iii. 

 p. 246 ; NyleX Jahresb. ii. d. Fortschr. d. Thicr-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, Virchoiv's Archiv, 1891, Bd. cxxv. S. 146 ; Schierbach, 

 Skandin. Arch. f. PhysioL, Leipzig, 1892, Bd. iii. S. 344; Ebstein u. Schulze, Virchwfs 

 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. 



