HAIR STRUCTURE OF THE MONOTREMATA 471 
sary to transfer the hair from the ether-alcohol solution to 95 
per cent alcohol, then to a solution composed of equal parts of 
95 per cent alcohol and the mounting oil, and then to the mount- 
ing oil itself. In each of these solutions the hair was allowed to 
remain for several minutes before transferring it to the mounting 
oil. The latter was often heated to 100°C. or thereabouts, to 
insure its penetration into all of the transverse ridges of the cutic- 
ular scales. 
Third method—clearing in balsam. Often the finer hairs were 
cleared and mounted in balsam. After having been washed in the 
ether-aleohol solution, they were dried and immersed in a bath 
of xylene and then transferred directly to a mount of very thin 
balsam. With hairs as those of the bats, shrews, and many of 
the rodents, this treatment proved to be the best. 
3. Sectioning and mounting. Transverse and longitudinal sec- 
tions of the larger spines, such as those of the spiny ant-eater 
(Tachyglossus hystrix) (figs. 52 to 56), were secured by fastening 
the spine between two pieces of very hard, firm-grained cork in 
an immovable fashion, and then filing the spine to the desired 
thinness with a smooth, parallel-grooved file. The section was 
then removed from the cork and ground gently upon a hone 
moistened with water to render the surface perfectly smooth, 
after which it was dehydrated in several alcohols, impregnated 
with xylene and xylene-balsam, and mounted in balsam in the 
usual way. ‘Those possessing the pithy type of medulla were 
differentially stained with eosin, the medulla taking the color, 
the firmer cortex and cuticle not. 
For hairs in general the usual processes of dehydrating, im- 
pregnating with xylene, paraffin-xylene, infiltration with paraf- 
fin, mounting on blocks, sectioning, staining, and mounting were 
employed. It was found advisable to use xylene and paraffin- 
xylene baths hot, and to keep them so in the oven, allowing the 
hairs to remain therein for several days each. In staining with 
eosin, safranin, gentian violet, or methyl green, the medulla always 
took the stain, the cortex and cuticle remaining uncolored. 
With most hairs, and more particularly with the finer ones, a 
very hard paraffin gave the best results. When it occurred that 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 27, No. 4 
