after absorption, could be used for rebuilding purposes, and which therefore might be regarded as a stage towards protein regeneration. They held that their view was strengthened by the fact that the increase of the excretion of nitrogen after the administration of leucine did not correspond with the amount of leucine fed, and further that an analogy existed in plant physiology where it was demonstrated that the decomposition products of protein, namely asparagine, leucine and tyrosine could be regenerated into protein when carbohydrate was also present. They suggested that a similar combination might occur in the liver of animals. Kutscher and Seemann (236) as the result of their experiments stated that they considered the above hypothesis very plausible, and concluded that the appearance of leucine and tyrosine, which they found, was the normal condition, and that these crystalline substances must be looked on as constituents, which, after absorption, would be utilized for the formation of tissue protein. They were unable to prove, however, that the hypothesis put forward by Salkowski and Leube was correct, as a series of experiments in which they performed a variety of Eck's fistula (cutting the liver out of the circulation), using a glass cannula for connexion between the portal vein and the vena cava, did not give decisive results.