SPECIFIC ACTION OF ENZYMES. 327 



Specific action of enzymes. The different enzymes are specific in 

 their action ; that is to say, each enzyme only acts on one class of 

 material and acts on it in a determinate manner, producing certain 

 specific substances as the result of that action. The table on p. 326 is 

 a classification of the digestive enzymes according to their specific action. 



Description of the digestive enzymes. The digestive enzymes 

 may be here most conveniently treated of according to their occurrence 

 in the various digestive secretions, because of the description of the mode 

 of their separation, where more than one is found in the same digestive 

 fluid. Their action on the different classes of foodstuffs and the products 

 formed thereby will be considered afterwards. 



Ptyalin. In the saliva of many animals, and especially in the herbivora, 

 a diastatic enzyme is found, to which, soon after the discovery that saliva 

 possessed such an action, 1 the name ptyalin was applied. In fishes 

 and in cetacea no salivary glands are present, 2 and in some other 

 animals the salivary secretion possesses no diastatic action ; for example, 

 the saliva of the dog has no diastatic action, and the same statement is 

 made for the typical carnivora in general. 3 In man, the secretion of both 

 the parotid and submaxillary glands has a diastatic action. At birth the 

 ferment is only found in the parotid ; it makes its first appearance in 

 the submaxillary two months later. 4 In the horse the secretion leaves 

 the parotid with the diastatic ferment still in the condition of a 

 zymogen, from which the enzyme is set free by treatment with alcohol 

 or by contact with unfiltered air. 5 



Ptyalin was first separated from saliva in an impure form by 

 Mialhe, 6 by precipitating filtered saliva with excess of absolute alcohol. 

 A scanty flocculent proteid precipitate is so obtained, which carries 

 down the ptyalin mechanically. Mialhe showed that this precipitate, 

 which was insoluble in strong alcohol, but partly soluble in water or 

 weak alcohol, possessed when dissolved the diastatic power of the 

 original saliva. From its supposed identity with the diastase of malt, 

 he called it diastase animal ou salivaire, and used the term ptyalin as a 

 synonym. It is now known that ptyalin and malt diastase, though 

 alike in their action upon starch, are not identical. This is shown best 

 by the difference in the reaction of the two enzymes to changes in 

 temperature. According to Roberts, 7 saliva possesses a maximum 

 action between the temperatures of 30 and 45 C., and, according to 

 Kjeldahl, 8 the optimum temperature is 46 C., while the enzyme is rapidly 

 destroyed by a temperature lying between 65 and 70 C. 9 On the 



1 Leuclis, Arch. f. d. ges. NaturL, Niirnberg, 1831 ; Schwann, Ann. d. Phys. u. Chem., 

 Leipzig, 1836, Bd. xxxviii. S. 358. 



2 According to Krukenberg ("Grundzlige einer vergleich. Physiol. der Verdauung," 

 1882, S. 67), in some fishes the secretion of the mucous glands of the mouth possesses a 

 diastatic action; the same is true of the mucous secretion of the frog's mouth. 



3 Griitzner, Arch. f. d. ges. Physiol., Bonn, 1876, Bd. xii. S. 285; Bunge, "Lehrbuch 

 der physiol. Chem.," Leipzig, 1894, Aufl. 3, S. 140; Neumeister, "Lehrbuch der 

 physiol. Chem., etc.," Jena, 1893, Th. 1, S. 122. 



4 Zweifel, " Untersuch. ueber den Verdauungsapparat. der Neugeborenen," Berlin, 

 1874. See also Schiffer, Jahresb. u. d. Fortschr. d. Thier-Chem., Wiesbaden, 1872, Bd. 

 ii. S. 205 ; Korowin, ibid., 1873, Bd. iii. S. 158 ; Bayer, ibid., 1876, Bd. vi. S. 172. 



5 Goldschmidt, Ztschr. f. physiol. Chem., Strassburg, 1886, Bd. x. S. 273. 

 I Compt. rend. Acad. d. sc., Paris, 1845, tome xx. pp. 654, 1483. 



7 " Digestion and Diet," London, 1891, p. 79. 



8 Abstract in Jahresb. ii. d. Fortschr. d. Thier-Chem., Wiesbaden, 1879, Bd. ix. S. 381. 



9 Roberts, loc. cit. ; Kiihue states that saliva loses its activity at a temperature of 

 60 C. ("Physiol. Chem.,"S. 21). 



