HAIR STRUCTURE OF THE MONOTREMATA 465 
recourse to some methods of staining or of otherwise rendering 
the scales more certainly visible. 
Second method—thickening the cuticular scales. Several 
methods of rendering the cuticular scales visible by treating the 
hair with reagents which thicken the scales, making them stand 
out from the cortex, are sometimes used. In the writer’s opinion, 
such methods cannot to advantage be employed where a careful 
determination of the exact scale form is the end in view. By a 
series of experiments he has become convinced that the use of 
caustic potash or soda, sulphuric acid, and so forth, which are 
recommended for use, often hot, distort the scales, and further- 
more cause them to bulge and to project outward from the cortex 
in an unnatural manner. This destroys at once both their char- 
acteristic outlines and their relationships one with another. 
Cuticular scales which have thus been dissociated from the cor- 
tex may, by pressure upon and a gentle rotation or agitation of 
the cover-glass, be entirely loosened from their connection with 
the remainder of the hair. Such seales are believed not to be 
useful for a careful correlative study of form. It was found 
that the following procedures might be used in the maceration of 
hairs for the dissociation of the cuticular scales where merely a 
crude notion of their form was the goal desired. Such scales re- 
vealed, in a general way, the arrangement patterns in which they 
were disposed about the hair shaft. These methods are: 1) heat 
gently in a 10 per cent aqueous solution of acetic acid until the 
hair shaft is slightly softened; 2) treat similarly, using a 1 per 
cent aqueous solution of chromic acid; 3) boil in a 5 per cent 
aqueous solution of hydrochloric acid. In each ease various 
trials are necessary before the requisite degree of softness of the 
hair shaft can be obtained. After any of these procedures, the 
hairs may be mounted in water before examination, in order that 
the scales may float outward and not cling tightly against the 
vortex. 
Third method—staining. The method which afforded the 
greatest measure of success, however, was one which was devised 
after the method of thickening the scales, and thereby distorting 
them, with caustics or acids, had been tried. The external sur- 
