STRUCTURE OF FEATHERS. 597 



Canada balsam, as may be thought preferable, the former men- 

 struum being well adapted to display the characters of the finer 

 and more transparent hairs, while the latter allows the light to 

 penetrate more readily through the coarser and more opaque. 

 Transverse sections of hairs are best made by gluing or gumming 

 several together, and then putting them into the section-instru- 

 ment ; those of human hair may be easily obtained, however, by 

 shaving a second time, very closely, a part of the surface over 

 which the razor has already passed more lightly, and by picking out 

 from the lather, and carefully washing, the sections thus taken off. 

 412. The stems of Feathers exhibit the same kind of structure 

 as hairs ; their cortical portion being the horny sheath that en- 

 velopes the shaft, and their medullary portion being their pith- 

 like substance which that sheath includes. In small feathers, 

 this may usually be made very plain by mounting them in 

 Canada balsam ; in large feathers, however, the texture is some- 

 times so altered by the drying up of the pith (the cells of which 

 are always found to be occupied by air alone), that the cellular 

 structure cannot be demonstrated, save by boiling thin slices in 

 a dilute solution of potass, and not always even then. In small 

 feathers, especially such as have a downy character, the cellular 

 structure is very distinctly seen in the lamince or "barbs," which 

 are sometimes found to be composed of single files or. pear- 

 shaped cells, laid end to end; but in larger feathers, it is usually 

 necessary to increase the transparency of the barbs, especially 

 when these are thick and little pervious to light, either by soak- 

 ing them in turpentine, mounting them in Canada balsam, or 

 boiling them in a weak solution of potass. In the feathers 

 which are destined to strike the air with great force in the act of 

 flight, we find the barbs fringed on each side with hair-like fila- 

 ments or pinnoe ; on one side of each barb these filaments are 

 toothed on one edge, whilst on the other side they are furnished 

 with curved hooks ; and as the two sets of pinnae which spring 

 from two adjacent barbs, cross one another at an angle, and each 

 hooked pinna on one locks into the teeth of several of the 

 toothed pinnae arising from the other, the barbs are connected 

 together very firmly by this apparatus of " hooks and eyes," 

 which reminds us of that already mentioned as to be observed 

 on the wings of Hymenopterous Insects ( 395). Feathers or 

 portions of feathers of birds distinguished by the splendor of 

 their plumage, are very good objects for low magnifying powers, 

 when illuminated on an opaque ground; but care must betaken 

 that the light falls upon them at the angle necessary to produce 

 their most brilliant reflection into the axis of the microscope ; 

 since feathers which exhibit the most brilliant metallic lustre to 

 an observer at one point, may seem very dull to the eye of 

 another in a different position. The small feathers of Humming 

 birds, portions of the feathers of the Peacock, and others of a 

 like kind, are well worthy of an examination; and the scientific 



