A new test for ergothioneine upon which is based a method for its estimation in simple solution and in blood-filtrates.

TANRET [1909] isolated from ergot of rye a base which he termed ergothioneine, which was shown by Barger and Ewins [1911] to be the betaine of thiolhistidine. There is no further record of the occurrence of ergothioneine in the plant or animal kingdom until the isolation of a substance from blood by Hunter and Eagles [1925, 1927], which has recently been shown by Eagles and Johnson [1927] to be identical with ergothioneine. The isolation of a similar substance from blood was also reported by Benedict, Newton and Behre [1926] and that substance has also been shown to be ergothioneine [Eagles and Johnson, 1927; Newton, Benedict and Dakin, 1927]. Two delicate colour tests for ergothioneine have been discovered in the course of recent work in this laboratory. One of these is that ergothioneine gives a blue colour in alkaline solution with the special phosphotungstic acid reagent used for the estimation of uric acid, but the test is not as specific as might be desired, as both uric acid and reduced glutathione also give a blue colour with this reagent. With suitable fractionation of tissue extracts however this test may yet prove of value for quantitative purposes. The new test to be described for ergothioneine is a special modification of the well-known diazo-reaction.