64 ENZYMES Oil SOLUBLE FERMENTS. 



kiiid_and relative amount of the several food-stuffs, the_changes 

 these undergo and the amount of alkaline secretions with which 

 they are mixed. Ail the evidence we do possess Igjids^ to the 

 belief that intestinal digestion to be of use must be capable ^f 

 being carried on in a mixture which may be alkaline, or_neutral, 

 or even frequently acid. Although the acidity of the intestinal 

 contents may be due to hydrochloric acid in the upper end of the 

 duodenum, the acidity is elsewhere much more probably due to 

 lactic or butyric acids, and it is interesting in this connection to 

 notice that according to Liudberger, 1 the former of these two 

 acids exerts a distinctly favouring influence on tryptic digestion, 

 especially in presence of bile and sodium chloride. Thus in 

 presence of '02 p. c. lactic acid and 1 2 p. c. bile and sodium 

 chloride fibrin may be digested more rapidly than in a neutral 

 solution and fully as quickly as in a solution of moderate alka- 

 linity. But the presence of -05 p. c. of lactic acid stops the 

 digestion. 



Traces of trypsin have been stated to be found in urine ; this 

 is somewhat doubtful. 2 



Trypsinogen. 



The zymogen of trypsin. Heidenhain first showed that the 

 pancreas contains, in its absolutely fresh and normal condition, 

 no ready-made enzyme, but an antecedent of the same. 3 This 

 body is readily converted into the active enzyme by the action of 

 dilute acids (1 c.c. of 1 p.c. acetic acid to each 1 grin, of gland- 

 substance) and a conversion also takes place if the gland is kept 

 for some time, especially in the warm, this resulting most prob- 

 ably from the spontaneous acidification which it thus undergoes. 

 The zymogen is soluble in strong glycerine without conversion into 

 the enzyme ; it is also soluble in water, in which it is gradually 

 changed into the enzyme, most rapidly when warmed, probably 

 under the influence of the acid reaction which the solution 

 acquires. 4 



Pialyn. 5 



In addition to the two pancreatic enzymes which have already 

 been described, both the secretion and the gland-substance contain 

 a third substance which has not as yet been isolated, of which, 

 therefore, but little is known from a chemical point of view, but 

 which must be regarded as an enzyme in virtue of the typical 

 conditions under which it is able to effect a hydrolytic decompo- 



1 loc. cit. ref. 1 , on p. 63. 



2 For litt. see ref. 1, sub Pepsin, on p. 61. 



3 Heidenhaiu, Pfliiger's Arch. Bd. x. (1875), S. 581. See also Podolinski, Ibid. 

 Bd. xni. (1876), S. 422. Weiss. Virchow's Arch. Bd. LXVIII. (1876), S. 413. 



* Kiihne, Lehrb. d. phi/siol. Chem. 1868, S. 120. 



6 From ir'ia.p = fat, and \vtiv = to split up or decompose. 



