2 lO 



NA rURE 



[June 29, 1,^93 



freed from grease, was shown lo yield its pigment lo pure water.] 

 1 ^oon found that alkaline liquids were more effeclive solvents 

 than pure water, and that the pigment could be precipitated from 

 its solution by the addition of an acid. [The pigment «as ex- 

 li acted from a feather by very dilute ammonia, and then pjecipi- 

 taied by adding excess of hydrochloric acid.] The next step 

 was to filter off the st-parated colouring matter, and to wash 

 and dry it. The processes of washing and drying are tedious, 

 and cannot be shown in a lecture. But the product obtained 

 was a solid of a dark crimson hue, non-crystalline, and having 

 (I purple semi-metallic lustre. I named it "turacin" (in a paper 

 published in a now long defunct periodical, The Student and 

 Inlcllccliial Observer, of April, 1868). The name was taken 

 from "Turaco," the appellation by which the plantain-eaters 

 are known — the most extensive genus of this family of birds 

 being Titraats. 



From the striking resemblance between the colour of arterial 

 blood and that of the red toiiraco feathers I was led to compare 

 iheir spectra. Two similar absorption bands were present in 

 •'Oih case-, l>ut their positions and intensities differed somewhat. 

 Naturally I bought for iron in my new pi;;ment. 1 burnt apor- 

 tion, dissolved the ash in hydrochloric acid, and then added 

 sodium acetate and potassium ferrncyanide. To my a'^tonish- 

 inent I got a precipitate, rot of Prussian blue, but of Prussian 

 iiiown. This indication of the presence of copper in lufacin was 

 confirmed by many tests, the metal itself being al-o obtained by 

 electrolysis. It was obvious that the proportion of copper 

 present in the pigmmt was very considerable — greatly in excess 

 of that of the iron (less than \ per cent.) in the pigment of 

 blood. 



Thus far two striking peculiarities of the pigment had been 

 revealed, namely, its easy removal from the weli of the feather, 

 and the presence in it of a notable quantity of copper. Both 

 facts remain unique in the history of animal pigment-. The 

 solubility was readily admitted on all hands, not so the presence 

 of copper. It was suggested that it was derived from the Bunsen 

 burner u«ed in the incineration, or from some preservative solu- 

 tion applied lo the bird-skins. 4nd it was asked, " How did 

 the copper gel into the feathers?" The doubters might have 

 sati.sfied themselves as to copper being normally and invariably 

 present by applying a few easy tests, and by the expenditure of 

 half-a-crown in acquiring a touraco wing. My results were, 

 however, confirmed (in 1872) by several independent observers, 

 including Mr. W. Crooke=, Dr. Gladstone, and Mr. Greville 

 Williams. And in 1873 Mr. Henry Bassett, at the request of 

 the late Mr. J. J. M'jnteiro, pushed the inquiry somewhat fur- 

 ther. I quote from Monteiro's " Angola and the River Congo," 

 published in 1875 (vol. ii. pp. 75-77): — "I purchased a large 

 bunch of the red wing-feathers in the market at Sierra Leone, 

 'with which Mr. H. Bassett has verified Prof. Church's results 

 conclusively," &c., &c. Mr. Bassett's results were published 

 jn the Chcmual News in 1873, three years after the appearance 

 of my research in the Phil. Trans. As concentrated hjdro- 

 chloric acid removes no copper from turacin, even on boiling, 

 the metal present could not have been a mere casual impurity ; 

 as the proportion is constant in the turacin obtained from 

 different species of touraco, the existence of a single definite 

 compound is indicated. The presence of traces of copper in a 

 very large number of plants, as well as of animals, has been in- 

 contestably established. And, as I pointed out in 1868, copper 

 can be readily detected in the ash of banana fruits, the favourite 

 food of several species of the " turacin-bearers." The feathers 

 of a single bird contain on the average two grains of turacin, 

 correspondirg to "14 of a grain of metallic copper; or, putting 

 the amount of pigment present at its highest, just one fifth of a 

 grain. This is not a large amount to be furnished by its food to 

 one of these birds once annually during the season of renewal 

 of its feathers. I am bound, however, to say that in the blood 

 and tissues of one of these birds, which I analysed immediately 

 . after death, I could not detect more than faint traces of copper. 

 The particular specimen examined was in full plumage ; I con- 

 clude that the copper in its food, not being then wanted, was 

 not assimilated. 



Let us now look a little more closely at these curious birds 

 themselves. Their nearest al lies are the cuckoos, with which they 

 were formerly united by .systematists. It has, however, been 

 long conceded that they constitute a family of equal rank with 

 the Cuculida;. According to the classification adopted in the 

 Natural History Museum, the order Picariae contains eight sub- 

 orders, the last of which, the Coccyges, consist of two families, 



NO. 1235, VOL. 48] 



the Cuculidje and the Musophagida:. To ihesame(.iiler beloftg 

 the Hoopoes, t';e Trogons, the Woodpeckers. Tht- iilamairv- 

 ealers, orMiis phagidse, are arranged in six genera and compriie 

 twenty-five species. In three genera — Turacus, Gilliitx, and 

 Musophaga — comprising eighteen species, and following one 

 another in zoological sequence, turacin occurs ; from tliree geneia 

 (seven species) — Corythaeola, Schizorhis, and CiymncischizcihU 

 — the pigment is absent. [The coloured illustrations 10 H. 

 .Schlegel's Monograph (Amsterdam, i860) on the Mu^ophajjidB 

 were exhibited.] The family is confined to Africa — lijjlit ol the 

 turacin-bearers are found in the west sub-region, one in the south- 

 west, two in the south, two in the south-east, four in the east, 

 two in thp central, and two in the north-east. It is notewonhy 

 that, in all these sub-regions save the south east, turacin-beaiers 

 are found along with those plantain-eaters which do not con- 

 lain ihe pigment. Oddly enough two of the latter species, 

 Schizorhis africaiia and .S. zonura, possess white palcljes desti- 

 tute of pigment in those parts of the feathers which m the turacin- 

 bearer.; are crimson. These birds do not — I will rot stiy cannot 

 —decorate these bare patches with this curiously complex pig- 

 ment. [Some extracts were here given from the late Mr. Mon- 

 teiro's book on Angola, vol. ii. pp. 74-79, and from leilers by 

 Dr. B. Hinde. These extracts contained re'erences lo curious 

 trails of the Touracos.] 



Usually from twelve to eighteen of the primaries or meiicarpo- 

 digitals and of the secondaries or cubitals amongst ihi; wing- 

 feathers of the turacin hearers have the crimson patches in their 

 web. Occasionally the crimson patches are limited tr sixer 

 seven of the eleven primaries. I have observed this parlicularly 

 with the violet plantain-eatei {Muiofhaga violacaa). In the«e 

 cases the crimson hea !-fealheis, which also owe their cclour 10 

 turacin, are few in number, as ifth-- bird, otherwise hrabhy, hud 

 been unable lo manufacture a sufficiency of the pigment. 1 m»y 

 here add that the red tips of the crest-feathers of Tiiriuus 

 meriani also contain tuiacin. 



In all the birds in which turacin occurs this pigment is 

 strictly confined to the red parts of the "eb, and is there unac- 

 companied by any other colouring matter. It is therefore found 

 that if a si' gle baib from a feather be analiscd, its black base 

 and its black termination possess no copper, while the inter- 

 mediate portion gives the blue green flash of copper when in- 

 cinerated in the Bunsen flame. [A parti-coloured featler was 

 burnt in the Bunsen flame with the result indicated.] 



Where it occurs I uracin is homogeneously distributee! in the 

 barlis, barbicels, and crochets of the web, and is rot found in 

 granules Or corpuscles. 



To the natural question, " Does turacin occur in any other 

 birds besides the touracos?" a negative answer must at present 

 be given. At least my search for this pigment in scores of birds 

 more or less nearly related to the Musophagida; has met with no 

 success. In some of the plantain-eaters (species of Turacus and 

 Gallirex) there is, however a second pigment closely related to 

 turacin. It is of a dull grass-green colour, and was n.Tnied 

 turacoverdin by Dr. Krukenberg in 1881. I had obtaired ibjs 

 pigment in 1868 by boiling turacin with a solution of caustic 

 sc:da, and had figured its characteiistic absorption band in my 

 first paper (Phil. Trans., vol. clix., 1870, p. 630, fig. 4). My 

 product was, however, mixed with unaltered turacin. But Dr. 

 Kiukenberg obtained what certainly seems to be the same pig- 

 ment from the green feathers of Turacus corythaix by treating 

 them with a two per cent, solution of caustic soda. I find, how- 

 ever, that a solution of this strength dissolves, even in the colij, 

 not only a brown pigment associated with turacoverdin, but ulti- 

 mately the whole substance of the web. By using a much 

 weaker solution of alkali (l part lo 1000 of water) a far better 

 result is obtained. [The characteristic absorption band of turaco- 

 verdin, which lies on the less refrangible side of D, was shown ; 

 also the absorption bands of various preparations of turacin.] 

 I have refrained from the further investigation of turacoverdin, 

 hoping that Dr. Krukenberg would complete his study of it. At 

 present I can only express my opinion that it is identical with 

 the green pigment into which turacin when muist is converted 

 by long exposure to the air, or by ebullition with soda, and 

 which seems to be present in traces in all preparations of isolated 

 turacin, however carefully prepared. 



A few observations may now be introduced on the physical 

 and chemical characters of turacin. It is a colloid of colloids. 

 And it enjoys in a high degree one of the peculiar properties ol 

 colloids — that of retaining when freshly precipitated, .an immense 

 proportion of water. Consequently when its solution in am 



