CHAP, i.] DIGESTION. 253 



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 

 digestion mixture be freed from the alkali-albumin by neutral- 

 isation, and after concentration by evaporation be treated with 

 excess of alcohol, most of the peptone will be precipitated. The 

 alcoholic filtrate when concentrated, gives, on cooling, crystals of 

 tyrosin, and the mother liquor from these crystals will afford 

 abundance of crystals of leucin. Thus by the action of the pan- 

 creatic 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, alkalis, or various oxidising agents. Now leucin is 

 amido-caproic acid, and thus belongs distinctly to the fatty bodies ; 

 while tyrosin is a member of the aromatic group, being closely 

 related to benzoic acid. So that in pancreatic digestion we have 

 the large complex proteid molecule split up into its constituent 

 fatty acid and aromatic molecules, and into its other less distinctly 

 known components. In gastric digestion such a profound destruc- 

 tion of proteid material occurs to a much less extent or not at all ; 

 neither leucin nor tyrosin can at present be considered as natural 

 products of the action of pepsin. 



Among the supplementary products of pancreatic digestion 

 may be enumerated a body which gives a violet colour with 

 chlorine water (this reaction is often seen in the juice itself), and 

 indol, to which apparently the strong and peculiarly faecal odour 

 which makes its appearance during pancreatic digestion is 

 due. Indol, however, unlike the leucin and tyrosin, is not a 

 product of pure pancreatic digestion, but of an accompanying 

 decomposition due to the action of organised ferments. A pan- 

 creatic digestive mixture soon becomes swarming with bacteria, in 

 spite of careful precautions, when natural juice or an infusion of 

 the gland is used. When isolated ferment is used, and atmospheric 

 germs are excluded, or when pancreatic digestion is carried on in 

 the presence of salicylic acid, which prevents the development of 

 bacteria and like organisms but permits the action of the trypsin, 

 no odour is perceived, and no indol is produced. 



After long-continued digestion, especially when accompanied by 

 putrefactive decomposition, the amount of proteids which are 

 carried beyond the peptone stage and broken up, may be very 

 great. 



On the gelatiniferous elements of the tissues in their normal 

 condition pancreatic juice appears to have no solvent action. In 



