44 
A. ZUNDEL. 
lation, but seldom when the animal is in pasture; and when it 
has existed it often disappears in the latter circumstances. 
The alternation of dampness and dryness also influences per¬ 
haps more the genesis of the disease than dryness alone. A foot 
too much impregnated with dampness, which is afterwards left to 
the air, becomes harder than a normal one placed in the same 
conditions. It retracts easier also. It is probable that the water, 
in softening the superficial layers of the wall, also renders the 
evaporation of the liquids of its deep parts more active. In the 
ordinary condition of the foot, the evaporation is diminished by 
the impermeability of the external hoof, which it owes to its den¬ 
sity ; but where this hoof is softened by maceration, its fibres, 
partly disintegrated by the dissolution of the glutinous sub¬ 
stance which keeps them as a compact mass, allow the air to 
pertetrate in their interspaces; air which drys them to a certain 
depth; hence a proportionate movement of retraction of the en¬ 
tire hoof upon itself. This evil effect of an excess of moisture 
explains how it is that poultices or other moist applications which 
horse attendants abuse so frequently, may give rise to results en¬ 
tirely opposite to the one in view, and why the hoof becomes dry 
and brittle, if not contracted. These topical applications take off 
from the cortical layer of the foot its protecting varnish, and ex¬ 
pose it to lose its water of growth. 
Some of the practices in shoeing contribute also to the desicca¬ 
tion of the hoof; such is principally that which consists in rasp¬ 
ing the wall from the coronary band to the plantar border; as 
also the too long continued contact of a hot shoe witli the 
foot. Shoeing itself promotes the same result, as, protected by a 
shoe, the foot no longer wears normally and grows beyond nor¬ 
mal limits. The mass of hoof, which, in the process of growth, 
has gone beyond the inferior limits of the podophyllous fissures, 
is no longer in contact with the living parts beneath, and they 
cease to be impregnated by the fluids which are thus constantly 
allowed to evaporate. It then dries up by evaporation and be¬ 
comes hard, and retracts upon itself in such a manner that the 
circumference of the foot in the lateral diameter diminishes more 
or less, especially posteriorly, and thus forces the incurvations of 
the sole and of the bars (H. Bouley). If a horse remains shod 
