13 



by boiling the feather in KOH, 0.5% and 

 then heating with chlorine, the dark matter 

 was completely broken up, and the feather 

 appeared colored as with the rusty- colored 

 tip which was apparently unaltered by the 



test. 



When compared to a feather wholly 

 changed to blue by the Aptosochromatic 

 process, a valuable suggestion is at once 

 thrown out, as to the nature of the change 

 of color. In a microscopic examination of 

 such a feather it is noticed that the lower 

 parts of the central barb colums were as in 

 the bicolored-fall feathers excepting that 

 the massing of the black appeared to be 

 denser. The upper parts however which 

 were deep orange brown before, varying to 

 lighter tints as the tips of the barbs were 

 approached, now appear thickly massed 

 with the black also, and the yellowish 

 barbules are likewise colored. The stream- 

 ing movement of the color granules is now 

 especially prominent in an actively chang- 

 ing feather, and it readily appears that the 

 rhachis gives up a part of its matter to the 

 barbs, which in turn supply it to the bar- 

 bules. A positive change of pigment is man- 

 ifested macroscopically, for a fall feather 

 held to the light or crushed, remains yel- 

 lowish in its yellow-colored parts, while a 

 spring feather, appearing entirely blue, so 

 treated, shows darkly, due to the addition 

 of black pigment. 



Undoubtedly the blue effects are pro- 

 duced by the prismatic column in coopera- 

 tion with the dark involved pigment, the 

 sheath enveloping these parts playing its 

 part with the barbules in producing the fall- 

 colored feather. A cross section of the blue- 

 producing barb sustains this view. When 

 placed under the microscope with all light 



