378 Proceedings of Royal Society of Edinburgh . [sess* 
solution of sulphuric acid, it is frequently found that one or more 
of the pigments goes into solution which is coloured, as do also the 
other constituents of the hairs, while another pigment sinks to the 
bottom undissolved. This result is similar to Sorby’s for black 
human hair, which contains a quantity of brown or red pigment, 
which colours on acid solution, the dominating black pigment, 
which causes the hairs to appear perfectly black, sinking to the 
bottom as a precipitate. This, however, I have not found to be 
the case with black horse hair, for when this is dissolved in strong 
acid, after the black pigment has sunk to the bottom, the acid 
solution remains perfectly clear and uncoloured. When white, or 
nearly white, horse or ass hairs are dissolved, the solution is also- 
clear, this result agreeing with Sorby’s for white human hair. 
The study, however, of the different sorts of pigment, whether in 
equine or other hair, and the application of the spectroscope to the 
problems presented, is the work of the chemist. 
In discussing hair coloration, it is well to remember that the 
tone of colour presented by the hairs collectively on the skin is 
often quite different to that of the individual hairs when viewed 
separately through the microscope. This must be due to the 
blending of the different shades of colour in the general effect. 
The colour of a hair is commonly supposed to depend on the 
presence or absence of the pigment granules of different shades in 
the cortex. This is, of course, largely the case. But there is often 
in addition a diffuse coloration throughout the cortex, and as 
above remarked, the colour of a hair is affected not inconsiderably 
by the degree of development of the medulla, and what is related 
to it, the presence or absence of air vacuoles in the medullary 
canal. 
A few remarks must be made concerning the shape of equine- 
hairs. Nathusius, in his investigations, made use of hairs from the 
shoulder region or from the side of the body, and remarks that in 
these, with the increasing thickness of the hair the cross section 
becomes more oval and less circular in shape. Thus the most 
circular sections are those through the medullaless regions near 
the point and root. In another place,* Nathusius appears to apply 
* Nathusius, “liber Haar-Formen und Farben von Equiden,” Landwirt- 
schaftliche Jahrbucher, Bd. xxvi., 1897, Berlin. 
