1890.] Study of Natural and Artificial Digestions. 



195 



4. When the starch is digested in very dilute solutions, the amount 

 changed may be approximately, though never quite, as great in a 

 flask as in the dialyser. 



5. The small amount of dextrin (4' 29 per cent.) which may be left 

 in the dialyser at the end of an active and prolonged digestion justi- 

 fies the assumption that under the more favourable conditions in the 

 alimentary canal the whole of the starch would be converted into sugar. 



6. There is no evidence from these experiments. o£ the formation in 

 appreciable amount of any sugar other than .maltose by the action of 

 saliva on starch. 



I am at present engaged on a set of experiments similar to the 

 above, using pancreatic ferment instead of saliva, in order to justify 

 my application of the results obtained with, the latter to the natural 

 process, as carried on by the former in the body. 



II.: — The Tryptic Digestion, of Proteids. 



The starting point for this series of experiments was found in the 

 following considerations. When proteids are digested by trypsin 

 artificially they always yield large quantities of leucin and tyrosin at 

 the same time as the peptones. In the intestine, on the other hand, 

 these crystalline products are not described as occurring in more than 

 microscopic amounts, if at all. Their absence in natural digestion 

 might be due to two causes : either (i) they are formed, but removed 

 as fast as they are formed ; or else (ii) they are not formed at all. 

 Since they arise by the further action of the trypsin on the first- 

 formed peptones, and the latter are removed very rapidly after their 

 formation, it was thus possible that the non-occurrence of leucin and 

 tyrosin in the intestine was due to the rapid removal of the material 

 out of which they otherwise would have arisen. It appeared possible 

 to obtain some solution of the difficulties presented by a comparison 

 of natural with artificial digestion by comparative experiments in the 

 dialyser and a flask- The solution is further one of considerable 

 physiological importance, in view of the fact that leucin is known to 

 be partly converted into urea when administered to. an animal, so 

 that the difference is one which- bears upon the possible source of 

 some of the urea which is normally being excreted under a proteid 

 diet. 



The material used for the digestions- was fibrin in different con- 

 ditions : 1. Boiled and extracted with alcohol and ether, in which 

 condition it is extremely difficult of digestion. 2. Simply boiled and 

 dried by pressure. 3. Air-dried without any preliminary boiling. 

 The digestive solution was in most cases prepared by dissolving 

 purified trypsin in 0'25 per cent, carbonate of soda with 0*5 per cent, 

 thymol ; in some few cases the fluid was prepared by adding Benger's 



