CHEMICAL BASIS OF THE ANIMAL BODY. 1193 



least in clogs, the reaction is faintly acid throughout, whether 

 they are fed on proteids or on a mixture of -carbohydrates and 

 fat. The acidity in the latter case is not surprising bearing 

 in mind the readiness with which the carbohydrates undergo a 

 lactic fermentation, especially inside the intestine, and it might 

 therefore have been abnormal in the dog whose food does not 

 normally contain carbohydrates. On the other hand in man, 

 living on a mixed diet, the possibility of a lactic fermentation 

 is always present. It is impossible to make any general state- 

 ment 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 intestinal 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 con- 

 nection to notice that 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 .alkalinity. 

 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 doutJtful. 



The pancreas contains, in its absolutely fresh and normal 

 condition, no ready-made enzyme but an antecedent (zymogen) 

 of the same. This substance 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 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 glycerin 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 influ- 

 ence of the acid reaction which the solution acquires. 



Lipolyn. 1 



In addition to the two pancreatic enzymes which have 

 already been described both the secretion and the gland-suh- 



1 From X/TTOS = fat and Xi5en = to split up or decom: 



