DIGESTION 333 



relation still more clearly implied in the fact that, although trypsin 

 readily forms albumoses and peptones from native protein when 

 such is offered to it, yet in natural digestion the great albumose- 

 and peptone-forming ferment is pepsin. In the lumen of the 

 intestine the trypsin is confronted mainly with protein already 

 hydrolysed to the albumose and peptone stage in the stomach. 



There is no reason to believe that there is any fundamental 

 difference between the action of trypsin and pepsin on the protein 

 molecule at any rate, up to the point of peptone formation. 



The order in which they appear and their relative amount at 

 different stages of the digestion show that the alkali-albumin 

 and the albumoses produced when trypsin acts in an alkaline 

 medium, such as a I per cent, solution of sodium carbonate, 

 are, like the acid-albumin and albumoses of peptic digestion, 

 mainly, at any rate, intermediate substances through which 

 protein passes on its way to peptone. In both cases the action 

 consists in a splitting up of the complex protein with assumption 

 of water, so that each successive product is further hydrated 

 than the last. Nor is it possible to point out any radical differ- 

 ence between the peptone of gastric and the peptone of pan- 

 creatic digestion. The further rapid hydrolysis of the peptone 

 by trypsin into decomposition products of low molecular weight 

 is a distinction merely of degree. For pepsin can also, as we 

 have seen, produce a certain amount of these after prolonged 

 digestion. Trypsin is a more powerful ferment than pepsin, 

 and naturally carries the decomposition farther, and accom- 

 plishes it with greater ease. 



In all that we have hitherto said regarding tryptic digestion 

 we have supposed that putrefaction has been entirely prevented. 

 If no antiseptic is added to a tryptic digest, it rapidly becomes 

 filled with micro-organisms, and emits a very disagreeable faecal 

 odour ; and now various bodies which are not found in the 

 absence of putrefaction make their appearance, such as indol, 

 skatol, and other substances, to which the faecal odour is due. 

 They are not true products of tryptic digestion, but are formed 

 by the putrefactive micro-organisms, which can themselves 

 split off from proteins numerous decomposition products, 

 including tyrosin, and change tyrosin into indol. 



Amylopsin, or pancreatic ptyalin, the diastatic or sugar- 

 forming ferment of pancreatic juice, changes starch into dextrin 

 and maltose, just as the ptyalin of saliva does. The two ferments 

 are possibly identical, but under the conditions of action of the 

 pancreatic juice its diastatic power is greater than that of saliva, 

 and it readily acts on raw starch as well as boiled. Amylopsin 

 is mainly, perhaps entirely, present in the juice in the form of 

 active ferment. If a zymogen stage exists, the mother-sub- 



