AN IMPROVED METHOD OF ASSAYING MELANIN IN FISHES

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Abstract
A method is described of preparing a solution (transparent colloidal suspension) of the melanin of fishes, and of assying this colorimetrically. The method includes hydrolysis of the tissues in a boiling alkaline solution, precipitation, centrifuging, further hydrolysis in acid and removal of acid and digestion products by dialysis; finally dissolving the melanin in dilute NaOH. Readings of the various samples were made with a tint-photometer, but a spectrophotometer could have been employed, perhaps, to advantage. For the interpretation of these readings, curves were drawn, based upon solutions of purified melanin of known concentration. The transmission "curve" of the various wave-lengths through such a melanin solution was likewise obtained by the use of a spectrophotometer. This proved to be a nearly straight line from a low point in the blue to a high point in the red. With lapse of time, alkaline "solutions" of melanin rather rapidly deteriorate, even in the dark, becoming increasingly transparent to all wave-lengths, but proportionately more to the red than would result from mere dilution.