ANATOMY AND PHYSIOLOGY OF THE HORSE , S FOOT. 93 
;s the amount of exercise, another is the nature of the ground 
over which the animals travel. It would appear, for ex¬ 
ample, that growth is more favorable on sandy than on 
argillaceous soils ; on turf than on artificial roads ; and with 
horses that perform a moderate amount of work than those 
that are overworked. In the first instance, the circulation 
in the generating tissue may be rendered more active from 
the greater salutary reaction of the ground ; while in the 
second this reaction may become too intense, and what was 
genial pressure on the turf, becomes on paved roads severe 
concussion, which disorders the circulation, induces more or 
less congestion of the secreting surface, and consequently a 
diminution in the supply of horn. Over-exertion brings 
about the same condition—congestion of the generating 
tissue and modified secretion. 
The influence of general diseases has not been closely 
observed, though it might be surmised that those morbid 
conditions which influence the epidermic and pilose growths 
would also produce analogous effects on the formation of the 
hoof. The relations between certain forms of derangement of 
the digestive organs and laminitis, with its hoof alterations, 
may be cited as a good illustration. 
It has been stated that growth is more rapid in warm 
than in cold countries, and in summer than in winter: 
the elevation of temperature and increase of vital energy 
accelerating it; while repair being proportionate to wear, 
the latter is greater on the hard dry soil of a hot climate 
than on the soft damp ground of a cold one. The balance 
between wear and repair is also exemplified in the case 
of a vigorous well-fed horse, and one that is ill-fed and 
feeble; in the first the hoofs grow strong and quickly, for to 
it exercise is absolutely necessary, but the other has less 
desire for movement, and therefore does not destroy so much 
horn. 
The part that nervous influence plays in determining the 
growth of the hoof has not yet, perhaps, been fully investi¬ 
gated, but that it has some power in the horn-forming process 
there cannot be a doubt. From personal observation I can 
testify that after the operation of neurotomy the growth of 
the hoof is increased, and that horses which, previous to the 
operation, had a somewhat feeble secretion of horn, and that 
not of the best quality, soon afterwards had larger and 
stronger hoofs* A horse of my own, with narrow feet and 
weak brittle hoof-walls, was operated upon in 1865 at Aider- 
shot, having become affected with navicularthritis in one 
foot through an accident. In 1866 the hoof of this foot. 
