On urobilin / by F. Gowland Hopkins and Archibald E. Garrod.

  • Hopkins, Frederick Gowland, Sir, 1861-1947.
Date:
[1898]
Catalogue details

Licence: Public Domain Mark

Credit: On urobilin / by F. Gowland Hopkins and Archibald E. Garrod. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    observation is open to the objection that the substance may have become altered by long keeping. More important even than such differences as the above is the fact that, as we shall presently point out, combustion analyses of the urinary and fsecal pigments show that hydrobilirubin and natural urobilin differ somewhat widely in their ultimate composition. The most striking difference is in the proportion of nitrogen, and as we shall show a determination of the nitrogen in hydrobilirubin gave us a figure agreeing very closely with that obtained by Maly. We are thus driven to the conclusion that the first of the two questions above propounded must be answered in a negative sense, and that the hydrobilirubin of Maly, whether it be a definite chemical individual or no, is not identical, either in its properties or in its composition, with natural urobilin. Passing on to the consideration of the further question we may say at once that the results which we have obtained by allowing the action of sodium amalgam to proceed further agree closely with those of Disqud and Eichholz. As the action proceeds the liquid assumes a pale yellow colour, the extra alkaline bands disappear and the precipitability of the urobilin-like product by hydrochloric acid is conspicuously diminished. When acidified, filtered and exposed to the air the liquid darkens and the absorption band gains in intensity. The product so obtained bears a far closer resemblance to the natural pigment than Maly's hydrobilirubin does. If an alkaline solution be acidified with acetic acid the urobilin-like substance may be precipitated, as natural urobilin is, by saturation with ammonium sulphate. In alcoholic solution with acetic acid it has a yellow or orange colour and shows a band like that of acid urobilin, with a more intense absorption towards red and a dark shading extending towards the violet. With ammonia the liquid assumes a pale yellow tint and, as Avith urobilin, the absorption band disappears. On the addition of sodium or potassium hydrate to alkalinity the band is seen narrowed and dis- placed towards red, and a similar single displaced band is seen with zinc chloride and ammonia, accompanied by the characteristic green fluorescence. We have endeavoured to obtain the product in as pure a condition as possible by repeated precipitation with ammonium sulphate and also by extraction with ether-chloroform by the method described in Part I. of this paper, but we have found that, even with the purest solutions