166 DISEASES OF THE HORSE’S FOOT 
coronet is hot and tender to the touch, and a sensation of 
warmth is sometimes conveyed to the hand by the horn of 
the surrounding parts of the wall. It is hardly necessary to 
say that, with accompanying conditions such as these, the 
sand-crack is a deep one. 
Where the lameness is but slight, we may attribute it 
almost solely to the pain occasioned by the mere wounding 
of the keratogenous membrane, and to no very extensive 
inflammatory changes therein. By some authorities this 
said to be due to the pinching of the sensitive structures 
between the edges of the fissure in the horny covering. In 
our opinion, however, pinching does not occur unless in- 
flammatory exudation into the sensitive structures adjoin- 
ing the crack has led to sufficient swelling to cause them to 
protrude. In other words, the movements of the horny 
box, communicating themselves to the structures beneath, 
and so occasioning movement in the wounded keratogenous 
membrane, are quite sufficient to give rise to the lameness 
without actual pinching of the structures implicated. 
The severity of the lameness will vary with the rapidity 
of the gait, and with the character of the road upon which 
the animal is made to travel. For instance, many animals 
in which the lameness is imperceptible at a walk become 
‘dead’ lame at a fast trot. It is sufficiently explained 
when one remembers the greater movements of expansion 
and contraction of the posterior parts of the wall brought 
about by the increase in the rate of progression. The same 
animal, too, will go distinctly more lame upon a hard than 
upon a soft surface. 
In like manner the lameness from toe-crack also varies in 
degree with the rate of progression and the character of the 
travelling, though not to such a noticeable extent as in the 
lameness from quarter-crack. A greater variation may in 
this case be brought about by moving the animal on 
ascending and descending ground. Descending an incline, 
with a more than ordinary share of the body-weight thus 
thrown upon the heels, the lameness is most marked. The 
reason would appear to be that the greater expansion of 
