Fatio on the Forms and Colours of Plumage. 381 



when the moisture was evaporated, a perfect sketch of the 

 barbs and barbules was traced upon the glass by a deposit of 

 greasy matter. 



In another case he wetted the feather with alcohol, but 

 still obtained the sketch in greasy matter, which he considered 

 to demonstrate that besides the coloured pigment, most of the 

 tissues contained a little colourless grease. 



Having satisfied himself that this diffused and colourless 

 grease did not act as a solvent of the pigment granules, to 

 which he ascribed a greasy nature, he made further obser- 

 vations thus described : — " I set to work to study and compare 

 under the microscope the basilar tubes (quills) of different 

 feathers in process of colouration, and I noticed always many 

 greasy colourless cellules in the tissue of the tube, in its inside, 

 and in the cortical substance of the parts nearest the stem, 

 close to the spot where many of the feathers exhibited a 

 marked strangulation. I could not, however, make out the 

 channels this grease must follow, and I endeavoured to dissolve 

 it on the field of the microscope. Having introduced a drop 

 of ether between the two glasses that enclosed the feather, 

 I saw like a circular canal, opening at the base of the 

 stem, and probably able to conduct the grease between the 

 remains of the subcutaneous sheath and the external wall of 

 the tube ; and I noticed within, a possible direct communi- 

 cation, between the hollow of the tube and the broad layer of 

 cortical substance which looked like a channel of porosity. 

 I speak now of small feathers, in which a less complete internal 

 desiccation may more easily allow this internal circulation of 

 greasy matter than the large feathers, in which the cortical 

 substance becomes more opaque and horny with lapse of 

 time." 



To test these suppositions, M. Fatio dipped the quill ends 

 of two small feathers in solution of carmine, having left one 

 intact, and stripped the barbs off half the stem of the latter. 

 At the end of twenty-four hours he found the carmine had 

 ascended either externally between the sheath and the quill, 

 or internally through the diaphragms formed by the cortical 

 substance. In the first feather the fluid had ascended com- 

 paratively little, because it was carried off laterally by the 

 barbs ; but in the second it rose up to the point at which the 

 barbs were left. 



M. Fatio in further pursuit of his analysis, " procured a 

 linnet whose breast feathers already showed a little of their 

 spring colours, and having delicately applied to them the 

 grease contained in the bird's oil-glands, soon perceived a 

 more intense colouration, which was increased by heat. This 

 colouration was not fugitive like that which grease or water will 



