The experiments were conducted with great care, and with as complete control as possible of the variable factors concerned. The investigators realised that, if any significance was to be attached to fluctuations in uric acid excretion following the intake of proteins and their derivatives, it was essential that accurate information be obtained as to the extent of the _variations_ to be expected _normally_ in the subjects when _fasting_. “Controls,” therefore, in which no food was consumed throughout the experiments, were instituted at frequent intervals so as to make sure that the level of endogenous uric acid metabolism was not altered by the long-continued _purin-free_ diet.[13] Passing now to the results obtained, it was noted that, after the intake of three types of _purin-free_ protein food (egg white, cottage cheese, and glidine), there ensued _a rise in uric acid output_, reaching its maximum during the third or fourth hour after their intake. No quantitative differences in the uric acid output after ingestion of these three types of protein were observed; in short, the findings did but confirm what had been repeatedly demonstrated, viz., that the _excretion of the endogenous uric acid is increased by purin-free protein food_. AMINO-ACIDS AND DICARBOXYLIC AMINO-ACIDS But the further interesting fact emerged, viz., that _glycocoll_ and _alanine_, end-products of protein digestion, also _augmented_ uric acid excretion; moreover, this even more swiftly than _proteins_, the maximum being reached within two hours after their intake. In addition, like results followed the ingestion of the _dicarboxylic_ amino-acids (glutaminic and aspartic acids), the increase in endogenous uric acid excretion being even more pronounced than with glycocoll or alanine. Now, it must be recalled that the _amino-acids_ represent the _end-products_ of protein digestion. Accordingly, Lewis and his co-workers argue that “since no digestive processes are required for the utilisation of amino-acids, it can hardly be considered that the _rises in endogenous uric acid_ observed following the ingestion of four different amino-acids can be attributed to the _work of the digestive glands_.” The effect, they held, is more probably attributable to “a direct stimulation of the body cells by amino-acids or their katabolism products, a stimulation of nuclear metabolism,” for it is known that amino-acids disappear very swiftly from the _blood-stream_ to be stored up temporarily in the _tissues_.