CHEMICAL BASIS OF THE ANIMAL BODY. 63 



possibility of a lactic fermentation is always present 1 . It is impossible 

 to make any general statement as to the reaction of the contents of 

 the small intestine ; it varies at different times, and depends upon the 

 kind and relative amount of the several food-stuffs, the changes these 

 undergo and the amount of alkaline secretions with which they are 

 mixed. All the evidence we do possess leads to the belief that in- 

 testinal digestion to be of use must be capable of 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 Lind- 

 berger 2 , 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 3 . 



Trypsinogen. 



The zymogen of trypsin. Heidenhain first showed that the pan- 

 creas contains, in its absolutely fresh and normal condition, no 

 ready-made enzyme but an antecedent of the same 4 . This body is 

 read'jy converted into the active enzyme by the action of dilute acids 

 (1 c.c. of 1 p.c. acetic acid to each 1 grm. of gland-substance) and a 

 conversion also takes place if the gland is kept for some time, especially 

 in the warm, this resulting most probably 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 5 . 



Pialyn 6 . 



In addition to the two pancreatic enzymes which have already 



1 According to Hammarsten the gastric mucus contains an enzyme which 

 converts lactose (milk-sugar) into lactic acid. See Maly's Bericht. Bd. n. (1872), S. 

 124. 



2 loc. cit. ref. 1, on p. 62. 



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



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

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



5 Kuhne, Lehrb. d. physiol. Chem. 1868, S. 120. 



6 From 7rtap = fat and Men/ = to split up or decompose. 



