196 



Dr. A. Sheridan Lea. A comparative [Feb. 20, 



" liquor pancreaticus " to the above solution of sodium carbonate and 

 thymol. 



The results of the experiments are as follows : — 



1. The rate at which the fibrin is broken down is enormously 

 greater in the dialyser than in a flask. 



2. The amount of proteid which goes into solution in a given time 

 is always greater in the dialyser than in a flask. 



3. The amount of leucin and tyrosin formed in a flask is greater 

 than in the dialyser, but the difference is comparatively slight. 



The third of these results made it possible that if, as in the 

 alimentary canal, the peptones could be removed nearly as rapidly 

 as they are formed, then the amount of leucin and tyrosin formed 

 m the dialjser would be also very small, and might approximate 

 to the traces formed in the intestine. This is a possibility to 

 which no experimental test can be applied, since the removal of 

 peptones is in artificial digestions dependent simply on their diffusi- 

 bility. In the alimentary canal their removal is, without doubt, 

 the result very largely of the specific activity of the epithelial 

 ceils. When I examined the contents of the intestine during 

 full proteid digestion, I obtained evidence of a very considerable 

 formation of leucin and tyrosin, of so much, in fact, that the difference 

 with respect to these substances in a natural and artificial digestion 

 becomes quantitative and not qualitative. Thus, in one case where a 

 large dog was fed with 500 grams of lean meat, of which nearly the 

 whole was digested in the ensuing six hours, I obtained such a 

 quantity of leucin and tyrosin from the contents of the small 

 intestine that, after the loss due to recrystallising and the perform- 

 ance of all the tests necessary for their thorough identification, I am 

 in possession of 1 gram of leucin and 0*3 gram of tyrosin. Although 

 the above is the most extreme case of the formation of these 

 substances with which I have met, still in all cases where I have fed 

 dogs with proteid, and this food has been perceptibly digested, I have 

 obtained more than "microscopic" amounts of leucin and tyrosin 

 from the intestine. Since there is no reason to suppose that active 

 absorption of these crystalline products has not been going on during 

 the whole time of their formation, their presence in some cases, in 

 not inconsiderable amounts, towards the close of a digestion must 

 imply a large total formation during the digestion. In this way the 

 difficulty arising out of a quantitative comparison of the crystalline 

 end-products of a natural and artificial tryptic digestion received a 

 solution of a quite unexpected kind. 



If, as I believe, my experiments thus show the formation of leucin 

 and tyrosin in not inconsiderable quantities during proteid digestion 

 in the intestine, some interesting considerations arise as to the physio- 

 iogical significance of the same. 



