92 ANATOMY AND PIITSIOLOGY OF THE HORSE J S FOOT. 
In harmony with the greater activity of the functions of 
the skin in horses at the advent of spring,—when the thick, 
long, woolly coat of winter disappears’ and is succeeded by 
the fine silky robe of summer,—the Keratogenous apparatus 
also evinces the influence of an exaggerated stimulus in its 
secreting an increased quantity of corneous material, which, 
as usual, forms a salient ridge around the upper border of the 
wall. This ridge on the hoof corresponds to the ring deve¬ 
loped at the same period at the root of the frontal horn in 
the bovine species. 
Age, as might be supposed, also produces its effects on the 
growth and quality of the hoof. In the young horse, we 
generally find that it increases more rapidly, and the texture 
is of better quality, than in many old animals, whose hoofs 
very frequently grow slowly, and are thin, brittle, and shelly. 
Iiest and exercise have also been noted as favorable or 
otherwise to the generation of horn, and it may be readily 
conceived a priori, that movement and the percussion of the 
feet on the ground will, by quickening the circulation in 
these organs, tend to produce a more rapid supply of that 
substance. Observation has demonstrated that among army 
troop-horses the hoofs grow faster during the season of 
manoeuvres, or while on the march, than when they have 
longer periods of rest in stables. This is indubitably shown 
by the difference in the length of time which the letters and 
figures burnt on each front hoof at its upper part take to 
reach its lower margin. In daily practice, apart from army 
experience, the same fact may be noted. If, for example, we 
take two horses of the same breed, age, colour, and size, 
and whose hoofs in the same conditions have an equal 
rate of growth, and subject one to regular work for a month, 
while the other remains idle, at the end of this period it will 
be necessary to remove more horn from the first than the 
second, in order to restore their feet to their proper length 
and position. As has been mentioned, the hoof grows faster 
when the horse is at liberty and unshod than when it is 
shod; the continual wear of the horn against the ground 
stimulates its reproduction; the destructive agent is at the 
same time the natural and energetic force at work in exciting 
growth, for in giving the shock that destroys it exalts the 
power that creates, enabling nature to maintain the equili¬ 
brium between reparation and deperdition. But whether 
the foot be shod or unshod, it is none the less true that 
exercise hastens the development of its protecting case ; 
though here again we have other influences intervening 
which modify, or even negative, the statement. One of these 
