56 ENZYMES OR SOLUBLE FERMENTS. 



substances by means of dialysis. 1 They possess further the re- 

 markable property of adhering with great tenacity to any finely 

 divided precipitate which is formed in the solutions in which 

 they are present, more particularly if the precipitate is of a viscid 

 or gelatinous nature. 2 It is not however possible to base upon 

 the above properties any general method of preparing the en- 

 zymes which is equally applicable to each of them; some are 

 most readily prepared in a fairly pure state by one method, some 

 by another, and very many by the conjoined application of two 

 methods. A further consideration must not be lost sight of in 

 connection with the separation of the enzymes from the parent 

 tissues ; thjs is the fact that in some cases the enzymes do not 

 exist in thlTfree and active conditions in tbp. p.plls of the reapec- 

 tive tissues, but in the form of an inactive antecedent, to which 

 the name of ' zymogen ' is usually applied. 3 Hence to obtain an 

 active extract it is frequently necessary to treat the tissue with 

 some such reagent as shall ensure the conversion of the zyrnogen 

 into the active enzyme. 



During prolonged digestions it is essential to insure the absence 

 of any changes due to the development of bacteria or other organ- 

 isms. The most suitable antiseptics for this purpose are salicylic 

 acid (*1 p.c.) and thymol ('5 p. c.). These reagents are dissolved 

 in a small quantity of alcohol and added in the above proportions 

 to the digestive mixture. 



It is frequently a matter of the utmost importance to determine 

 whether the hydrolytic power of any given preparation is due to 

 the action of a soluble enzyme or of a ferment (organised). The 

 discrimination is most readily effected by carrying on the diges- 

 tion in presence of chloroform, which is inert towards the enzymes 

 but inhibits the activity of ferment organisms. 4 



SPECIAL DESCRIPTION OF THE MORE IMPORTANT ENZYMES. 5 

 Ptyalin. 



While occurring chiefly and character! stir.g,,1]y i" gallon ^ a similar 

 enzyme may be obtained in minute amount, but fairly constantly, 

 from almost any tissue or fluid of the body, more particularly in 

 the case of the pig. It was first separated out from saliva, but 

 in an impure condition, by Mialhe, who precipitated the saliva 

 with an excess of absolute alcohol. 6 It has been prepared in the 



1 Maly, Pfluger's Arch. Bd. ix. (1874), S. 592. 



2 Briicke, Sitzb. d. Wien. Akad. Bd. xnn. (1861), S. 601. Danilewsky, Vir- 

 chow's Arch. Bd. xxv. (1862), S. 279. Cohnheim, Virchow's Arch. Bd. xxvm. 

 (1863), S. 241. 



3 Heidenhain, Pfliiger's Arch. Bd. x. (1875), S. 583. 



4 Miintz, Compt. Rend. T. LXXX. (1875), p. 1255. 



5 Consult the article ' Fermente' by Emmerling in Ladenburg's HandwOrterbuch 

 d. Chem. Bd. iv. 1887, S. 95. 



6 Compt. Rend. T. xx. (1845), pp. 954, 1485. 



