XXI. Researches on turacin, an animal pigment containing copper

Origin of the present Inquiry.—The stability of the colours which the feathers of birds display has been repeatedly proved. These colours are due either to what we may call the optical character of the surfaces of the web, or to the presence in it of definite colouring-matters. These pigments may be opaque like enamel, or translucent and permeating the substance of the barbs; they have been as yet but very imperfectly studied. In a few instances only have they been actually separated from the structures containing them, while in no case have they been completely examined from a chemical point of view. So far as I can learn, we have no exact information as to the amount and the deportment, chemical constitution and reactions of those substances which M. Bogdanow, some twelve years ago, succeeded in extracting from the feathers of many birds, and notably from the red feathers of Calurus auriceps and Catinga cærulea. Before giving an outline of my own experiments in this direction, I will mention the particular circumstances which led to the prosecution of the present research. A few years ago Mr. W. B. Tegetmeier pointed out to me a singular property of the red feathers of the bird called the Touracou, or Plantain-eater. These feathers yield up a part of their colouring-matter to pure water, a beautiful rose-coloured solution being thus obtained. Mr. Tegetmeier’s attention had been drawn to this fact, and he at once perceived that it was worthy of fuller investigation than it had already received. On further inquiry, I find that Mr. Ward of Wigmore Street had noticed the evanescence and solubility of the red tint in question many years ago, and that other observers, within the last few years, have even succeeded in staining pieces of paper with the red solution which these feathers yield. In order that it may be seen what was the position of the inquiry when I commenced in 1866 my experiments on this subject, I may cite the authority of some private letters which have been placed at my disposal through the courtesy of Mr. Hugh Owen. These letters were written by Dr. Benjamin Hinde, principal Medical Officer on the Military Staff at Bathurst, on the Gambia. In one of his letters, dated May 1865, Dr. Hinde enclosed a piece of paper stained with the red pigment of 1 inch of a feather of the violet Plantain-eater, Musophaga violacea. He says that the moment soap touches the feathers the colour runs, but that it is difficult of extraction with pure water. But he adds, “the birds I sent home washed themselves nearly white in the water left for them to drink!” In a subsequent letter Dr. Hinde gives some details concerning the different species of Plantain-eaters, and says, with reference to the feathers he had previously sent to England, “all the feathers sent were from the same bird and grew in this house.” This fact negatives any idea of an artificial dye being present in the feathers, and is further referred to in the following memoranda by Mr. Hugh Owen:—”A pair of violet Plantain-eaters from the Gambia were sent over to a friend in Ireland by Dr. Hinde. The birds arrived in excellent condition, and were speedily provided with ample space and all appliances for cleanliness. For a while this splendid plumage, the deep crimson patch on the dark violet of the wing, excited continual admiration. After a day or two the crimson faded; in a few more the colour changed to a pale and dirty grey. The disappointed owner wrote an account of this change to Bathurst, concluding, of course, that the natives had imposed on Dr. Hinde by selling him a pair of painted birds: this, however, was impossible; there was no mistaking the peculiar and shield-shaped bill or the legs of the Musophaga. Whatever change had taken place, the birds were genuine Touracous. Without delay another bird was procured, so young as to be only partly fledged, the wings only in the pinfeathers. As soon as these were sufficiently grown, the experiment was repeated, and the colour found to be inconstant and capable of extraction.” The data already given, and many others with which I have been subsequently furnished, incontestably prove the normal presence, in some of the feathers of the Plantain-eater, of a red pigment soluble in water, and still more readily dissolved by soap. I may now give my own results as to the preparation and physical and chemical properties of this new red animal pigment.