CH. XI.] HOW FAR DOES DECOMPOSITION OF PROTEIDS PROCEED? 445 



found that pepsin was more rapidly destroyed by a solution of sodium 

 carbonate containing trypsin than in one free from it, and discovered that 

 pepsinogen also appeared to be destroyed in the same manner. 



Were it not for the arrest of peptic proteolysis, the intestinal 

 digestion by the pancreatic trypsin would be impossible. With the 

 admixture, then, of the acid chyme with the bile and with the 

 pancreatic juice, the first act in the great process of digestion may be 

 said to come to an end. 



We have devoted so much space to a consideration of the action 

 exerted both by the bile and the pancreatic juice on the various 

 groups of food constituents that it is only necessary in this place to 

 emphasize certain facts as of special importance, and to supplement 

 them by referring to others which have inadvertently been omitted. 



Digestion by trypsin as it proceeds in the intestine resembles 

 an aseptic pancreatic digestion as conducted in vitro, with the aid 

 of such agents as thymol and salicylic acid, rather than one occur- 

 ring in the presence of putrefactive bacteria. We have seen that the 

 contents of the small intestine are destitute of putrefactive odour, 

 that they are normally destitute of the micro-organisms which lead 

 to the production of indol, skatol, skatol-carbonic acid and phenols, &c. 

 The interesting question remains, however, how far, in the physio- 

 logical condition, does the decomposition of the albuminous molecule 

 proceed under the influence of trypsin ? We have seen that, in vitro, 

 the albuminous bodies rapidly split up into albumoses and peptones, 

 and that the latter even in the absence of all organisms, undergo, in 

 part, ready decomposition, yielding as principal products amido-acids, 

 lysine and lysatinine and tryptophan. It appeared probable enough 

 that in the conditions existing in the alimentary canal the decompo- 

 sition might not proceed so far that hemipeptones and antipeptones 

 once formed, might, either as such or as regenerated albumins, pass 

 through the intestinal wall, without undergoing further degradation. 

 The experiments of Sheridan Lea have shewn that even in the normal 

 living alimentary canal of the dog, a fraction of the peptones, and 

 not altogether an insignificant one, undergoes the decomposition 

 which leads to the setting free of the amido-acids 1 . On the other 

 hand, Macfadyen, Nencki and Sieber failed to find leucine and 

 tyrosine in the contents of the ileum and explained the fact on the 

 hypothesis that the lactic acid, which is generated through the 

 instrumentality of the micro-organisms, modifies the activity of 

 trypsin-digestion sufficiently to prevent so profound a decomposition 

 of the albuminous molecule as is implied by the appearance of the 

 amido-acids. 



In so far as the action of the diastatic enzyme of the pancreas is 

 concerned, we may now, with confidence, assert that it results in the 

 formation of maltose, and that it is not capable of breaking down this 



1 Sheridan Lea, 'A Comparative Study of Artificial and Natural Digestion,' Journ. 

 of Physiology, Vol. xi. (1890), p. 227 et seq. 



