sensitive laminæ are both portions of the same thing--namely, a modified
skin, in which the epidermis is represented by the horny laminæ, and the
corium by the sensitive--it is clear to see that the cells covering the
inspreading horny laminæ are dependent for their growth and reproduction
upon the cells with which they are in immediate contact--namely, those
of the sensitive laminæ--and that therefore the sensitive laminæ are
responsible for the growth of the horny.


B. CHEMICAL PROPERTIES AND HISTOLOGY OF HORN.

Horn is a solid, tenacious, fibrous material, and its density in the hoof
varies in different situations. It is softened by alkalies, such as caustic
potash or soda and ammonia, the parts first attacked being the commissures,
then the frog, and afterwards the sole and wall. Strong acids, such as
sulphuric acid and nitric acid, also dissolve it.

The chemical composition of the hoof shows it to be a modification of
albumin, its analysis yielding water, a large percentage of animal matter,
and materials soluble and insoluble in water. The proportions of these, as
existing in the various parts of the hoof, have been given by Professor
Clement as follows:

Wall. Sole. Frog.
Water 16.12 36.0 42.0
Fatty matter 0.95 0.25 0.50
Matters soluble in water 1.04 1.50 1.50
Insoluble salts 0.26 0.25 0.22
Animal matter 81.63 62.0 55.78