BILE, PANCREATIC JUICE, AND SUCCUS ENTERICUS. 283 



activity of an alkaline juice is hindered or delayed by neutralization and 

 arrested by acidification, at least with mineral acids. The glycerin extract 

 of pancreas is under all circumstances as inert in the presence of free mineral 

 acid as that of the stomach in the presence of alkalies. If the digestive 

 mixture be supplied with sodium carbonate to the extent of 1 per cent., 

 digestion proceeds rapidly, just as does a peptic mixture when acidulated 

 with hydrocholoric acid to the extent of 0.2 per cent. Sodium carbonate of 

 1 per cent, seems in fact to play in tryptic digestion a part altogether com- 

 parable to that of hydrochloric acid of 0.2 per cent, in gastric digestion. 

 And just as pepsin is rapidly destroyed by being heated to about 40 with 

 a 1 per cent, solution of sodium carbonate, so trypsin is rapidly destroyed 

 by being similarly heated with dilute hydrochloric acid of 0.2 per cent. 

 Alkaline bile, which arrests peptic digestion, seems, if anything, favorable 

 to tryptic digestion. 



Corresponding to this difference in the helpmate of the ferment, there is 

 in the two cases a difference in the nature of the products. In both cases 

 peptone is produced, and such differences as can be detected between pan- 

 creatic and gastric peptones are relatively small ; but in pancreatic digestion 

 the by-product is not, as in gastric digestion, a kind of acid-albumin, but, 

 as might be expected, a body having more analogy with alkali-albumin. 

 Moreover, before the alkali-albumin is actually formed, the fibrin becomes 

 altered and takes on characters intermediate between those of alkali-albumin 

 and of ordinary albumin ; and when fresh raw, i. e., unboiled, fibrin is acted 

 upon by pancreatic juice, one or more globulins appear as initial products. 



Further, there are evidences that differences of even a more profound 

 nature than the above exist between pancreatic and gastric digestion. One 

 of these is the appearance in the pancreatic digestion of proteids of two 

 remarkable nitrogenous crystalline bodies, leucin and tyrosin. When fibrin 

 (or other proteid) is submitted to the action of pancreatic juice, the amount 

 of peptone which can be recovered from the mixture falls far short of the 

 original amount of proteids, much more so than in the case of gastric juice ; 

 and the longer the digestive action, the greater is this apparent loss. If a 

 pancreatic digestive mixture be freed from the alkali-albumin by neutraliza- 

 tion and filtration, the filtrate yields, when concentrated by evaporation, a 

 crop of crystals of tyrosin. If these be removed the peptone may be pre- 

 cipitated from the concentrated filtrate by the addition of a large excess of 

 alcohol and separated by filtration. The second filtrate, upon being concen- 

 trated by evaporation, yields abundant crystals of leucin and traces of 

 tyrosin. Thus, by the action of the pancreatic juice, a considerable amount 

 of the proteid which is being digested is so broken up as to give rise to 

 products which are no longer proteid in nature. From this breaking up of 

 the proteid there arise leucin, tyrosin, and probably several other bodies, 

 such as fatty acids and volatile substances. 



As is well known, leucin and tyrosin are the bodies which make their 

 appearance when proteids or gelatin are acted on by dilute acids, alkalies, or 

 various oxidizing agents. Leucin is a body which, in an impure state, crys- 

 tallizes in minute round lumps with an obscure radiate striation, but when 

 pure forms thin glittering flat crystals. It has the formula C 6 H 13 NO 2 or 

 C 5 H 10 .NH 2 (CO.OH), and is amido-caproic acid. Now, caproic acid is one 

 of the " fatty acid " series, so that leucin may be regarded as a compound of 

 ammonia with a fatty acid. Tyrosin, C 9 H n NO 3 , on the other hand, belongs 

 to the "aromatic" series ; it is a phenyl compound, and hence allied to ben- 

 zoic acid and hippuric acid. So that in pancreatic digestion the large com- 

 plex proteid molecule is split up into fatty acid and aromatic molecules, 

 some other bodies of less importance making their appearance at the same 



