116 



THE OSPEEY. 



Without doubt we have here a blue-pro- 

 (liiciiifT structure wliich couibiued with the 

 yellow stain results in g-reen. This point was 

 admirably shown on section through a green 

 feather at an angle of 45 degrees witli tlie 

 barbs, so that a thin layer of the yellow cov- 

 ered the inner structure at one point and a 

 thicker laj'er at another point. Under the 

 microscope diH'crent shades of green, from 

 very pale to the normal tone, were to be seen, 

 according to the thickness of the yellow stain; 

 and in places where the underlying colors 

 were exjiosed a deep, almost indigo, color was 

 seen. 



AVhcn color change begins to he nuinifestcd 

 in a green featlier, the only perceptible ac- 

 tivitj' is in the small part of the feather un- 

 dergoing the alteration, and it is not till an 

 intermediate stage is reached, as in Fig. 3, 

 that the whole of the feather becomes dis- 

 turbed. Gradually, as if by a slow dissolving 

 process, the dark coloring leaves the barbules; 

 next, the central cellular structxires of the 

 barbs are disarranged; and finally, the floccu- 

 lated masses of the rhachis disappear. Thus 

 from a green feather a yellow one results, 

 microscopically free from every other 

 color than yellow, ex-cej^ting for the 

 now pale columns of the barbs and 

 heavy mass of the rhachis. Strong evi- 

 dence that the superstructure of the feather 

 is thus broken up is afforded by the single test 

 of transmitted light. A feather changed from 

 green to yellow shows true in such lig'ht The 

 crushing of such a feather gives the same re- 

 sult, excepting, of course, for a slight deep- 

 euing of the hues of the yellow feather where 

 the underlying pigment, chemically proved to 

 be red, is brought into prominence. This red 

 gives a density to the yellow, as is evident 

 when the zoonerythrin (red) is dissolved out; 

 for the yellow then appears paler. A feather 

 which has turned yellow, when treated with 

 '/j per cent solution of KOII gave little or no 

 result: biit xipon submitting a green feather 

 to such a test, complete decoloration resulted. 

 Apparently this indicates that, as caustic pot- 

 ash affects zoomelanin (black), and a green 

 feather treated with this reagent is discol- 

 ored, while a yellow feather so treated is not 

 changed, the blue-producing structure de- 

 pends largely on this black pigment; and also 

 that, in the process of color change of the 

 feather, there is a coTuplete alteration in the 

 relativepro|)ortionsof the|)ignu'nts concerned. 

 This last conclusion is confirmed by treating 

 a yellow-changed feather with ether, when 

 the central red is almost completely removed, 

 only a few undetermined granules remaining. 

 Thus the main point to be considered is, that 

 red and black, together with a superstructure 

 capable of producing green in connection with 

 the }-eltow stain, are present in the green 

 feathers; that under vital conditions this black 

 pigment, together with the particular super- 

 struct\ire, is broken down from its former 

 condition and destroyed. To produce such re- 

 sults as these there must have been very de- 

 cided changes, both in the surface structure 

 and in the pigmentation of the individual 

 feather which has turned from green to yel- 

 low. The whole matter looks much like a 

 ripening process in certain feathers, which 



thus change color; and it is curious that only 

 some feathers, as of the head, and not those 

 of other green parts of the plumage, should 

 suffer such profound metachrosis. That the 

 color change from green to yellow is an ac- 

 tual phj'sical modification of the substance of 

 the feather, is shown by the fact that such 

 a yellow-turned feather is identical under the 

 microscope with any yellow" feather wliich is 

 of this color from the start; that is, an apto- 

 Bochromatically yellowed feather is indistin- 

 guishable from an orig'inally yellow one which 

 sprouts during the moidt. 



In aptosochromatic feathers an active move- 

 ment was evident, for the tips of the barbules, 

 formerly occupied by the dark masses, in the 

 preen stage of the feathers, became filled with 

 tlie yellow in the changed feathers. In view 

 of this fact, it does not seem uni-easonable to 

 suppose that an additional amount of pigment 

 mayliave been supplied, either indirectly from 

 the body of the bird or directly as a 

 result of chemical activity in the feath- 

 er itself; but this is a matter into 

 which I can not at present enter, and just how 

 the change takes place is left for wiser heads 

 than mine to discover. The phenomenon may 

 possibly be dependent iipon a process of retro- 

 grade metamorphosis or catabolism, in con- 

 nection with some solvent action of certain 

 fluids supplied to the feather from the bird's 

 body in varj'ing quantity and quality. Some 

 hint of the mode of supplying pigment to a 

 growing feather was afforded under the mi- 

 croscojie. In an immature feather, yellow 

 from the start, no coloring was to be seen till 

 the rhachis was reached, at the point where 

 a mass of coloring was being deposited, and 

 granular matter could be seen flocculating in 

 all directions. This feather when plucked 

 emitted a drop of colorless fluid from the 

 umliilicus inferior, and that this fluid should 

 contain the pij^nneuts in solution, to be pre- 

 cipitated in the rhachis and vanes, is not im- 

 Iio.ssible. The accurate determination of this 

 point would greatly assist in the comprehen- 

 sion of aptosochromatism. 



Cross section of a g'reen feather displa.yed 

 under the microscope the arrangement of the 

 structure and coloration. Starting from the 

 exterior of the section, first a laj'er of yellow 

 ^vas seen, and then in the center was a col- 

 lection of cellular bodies tliickly massed with 

 color granules. It appeared in many cases 

 that tlu'se granules were external to the cell- 

 like bodies, and again, that they formed a 

 part of the internal composition of the latter. 

 The whole subject offers a most attractive 

 field for observation and speculation, as the 

 subject has been fully treated by no one, so 

 far as I know. 



In brief, the main points now made are 

 these: (1) That color change of jjlumage 

 without feather loss enough to constitute a 

 moult is a fact; aptosochromatism is demon- 

 strated to be true. (2) That color change in 

 the individual feather is an indisputable fact. 

 (S) That this change in the present instance 

 depends upon vital conditions within the oi'- 

 gani.sm. inasiuuch as it is known to cease af- 

 ter death. (4) That aptosochromatism and 

 moult are tw-o distinct and independent pro- 

 cesses, though they may be concurrent, or 



