Concerning this point, Lea[194] has recently reported some experimental evidence obtained by a comparative study of artificial pancreatic digestion as carried on in a flask, with similar digestions carried on in parchment dialyzer tubes, the latter so arranged that the diffusible products of proteolysis can pass from the tube into the surrounding fluid. As Lea justly says, this whole question of the formation of leucin by proteolysis is a very important one, since it bears closely upon one of the possible methods by which urea may be quickly formed from proteid food. Thus, we have evidence that when leucin is administered to mammals a portion of its nitrogen, at least, quickly reappears as urea and uric acid in the urine.[195] Further, there is a certain amount of evidence that this transformation takes place in the liver, viz., in the organ where leucin absorbed from the intestine would naturally be first carried.[196] [194] A Comparative Study of Artificial and Natural Digestions. Journal of Physiology, vol. xi, p. 226. [195] E. Salkowski: Weitere Beiträge zur Theorie der Harnstoffbildung. Zeitschr. f. Physiol. Chem., Band 4, pp. 55 and 100. [196] W. Salomon: Ueber die Vertheilung der Ammoniaksalze im thierischen Organismus und über den Ort der Harnstoffbildung. Virchow’s Archiv, Band 97, p. 149. Obviously, the main point to be gained in a dialyzer-experiment is the removal of the soluble products of digestion as soon as they are formed; but peptones are not rapidly diffusible, and the process, as noted under the head of gastric digestion, cannot be considered in any sense as yielding the same results as might be obtained in the living intestine. Still, the method offers a closer approach to the natural process than when carried on in a flask, and the results are of interest. Thus, Lea finds in the first place that in a dialyzer-digestion the proteid is more quickly dissolved, and that there is far less tendency for the formation of an insoluble antialbumid with its natural resistance to the ferment. Still, it is to be noticed that the amount of this antialbumid-residue formed by trypsin-proteolysis in a flask is mainly dependent upon the strength of the ferment solution, and the character of the proteid undergoing digestion. If the latter is in a fairly digestible form, and the enzyme solution reasonably active, then even the flask-digestion may show almost no residue of antialbumid. Yet there is at least a shade of difference in the two cases, which may be expressed by the statement that trypsin-proteolysis, as carried on in a dialyzer-tube, is prone to give less insoluble antialbumid than a corresponding digestion in a flask. Further, the amount of leucin and tyrosin formed in a flask-digestion is always greater than in a dialyzer-digestion, other conditions being equal. Naturally, these results help us very little in drawing any conclusions regarding the extent to which leucin and tyrosin may be formed in the intestine.