HAIR STRUCTURE OF THE MONOTREMATA 467 
was obtained by soaking the whole hair (after washing in the 
ether-alecohol solution) for several minutes in a 10 per cent aque- 
ous solution of caustic soda, yet not long enough to render the 
hair slimy or to distort the scales, and then dipping it into a 
pink solution of safranin and 82 per cent alcohol. ‘The entire 
surface of the hair assumed a pink color, and while the scale 
sculpturings over the surface of the hair were obliterated by the 
uniformity of the coloration, yet the profile of the hair shaft stood 
out with great clarity against the white light of the microscopic 
field, or even more strikingly against the black background when 
very oblique illumination and a low-power objective were util- 
ized. This manipulation was often resorted to to determine the 
relation of the transverse scale sculpturings on the surface of the 
hair to the profile of the serrate edge. 
For immediate examination the hairs stained to show the scale 
sculpturings on the surface were put into temporary dry mounts 
by fastening over them a cover-glass touched about its edges with 
balsam. Permanent mounts were obtained by ringing the cover- 
glasses with cement upon a turn-table. They were often, for im- 
mediate use, also mounted in very viscous gelatin gum dammar, 
or balsam. It was found that if very fluid balsam, dammar, or 
gelatin were used, the coloring material was quickly dissolved 
from out the scale depressions and distributed throughout the 
whole of the mounting medium. For the coarser hairs dry 
mounts were the most successful; for the finer, the glycerin, bal- 
sam, and dammar mounts. 
It was frequently found desirable to trace completely around 
the hair the course of the markings indicating the edges of the cutic- 
ular scales, particularly in the study of the form of the coronal 
type of scales. To render the rotation of the hair under the high- 
est powers of the microscope practicable, the apparatus shown in 
figure A was devised, and termed ‘hair rotator.’ It was con- 
