156 ANATOMY AND PHYSIOLOGY OP THE IIORSE^S FOOT. 
In explanation of the notable diminution in the growth 
from the 3rd to the 20th of November, the regeneration of the 
primitive nerve-tubes cannot be invoked, as this diminution 
was also observed in the healthy foot. 
The identity in many respects between the horn and hair 
induced Grohn to make experiments to ascertain what in¬ 
fluence the nerves exercise on the growth of the latter. On 
the two experimental horses—two and four—the hair was 
shaved off on the healthy and neurotomised limbs to a certain 
extent above the coronet, and in such a manner that the part 
shaved was soft and smooth to the touch, and perfectly supple. 
On the second horse this shaving was performed sixteen days 
after the neurotomy; on the fourth, only four days subse¬ 
quently to the operation. In these two horses there was no 
subsequent recovery of sensation. 
Two days after the hair had been cut, it had already 
grown so fast on the neurotomised limbs that it could be seen 
and felt. There was nothing of this on the healthy legs 
until the fourth day, when the hair on them was about 
the same length it was on the others on the second day; 
while the hair on these latter had grown a millimetre in 
length. 
It was remarked, that the difference in growth was greater 
in the second than the fourth horse. 
According to these experiments, it would appear that the 
horn grows all the faster on feet in which the loss of sensation 
is complete, and that as soon as this is more or less re-esta¬ 
blished, the growth diminishes. Grohn adds, that after the 
removal of a portion of the wall, its regeneration is all the 
more rapid in proportion to the number of nervous filaments 
cut or destroyed. 
In the fourth experiment it was also remarked that, if from 
the 3rd to the 20th of November, the inner part of the hoof 
belonging to the neurotomised limb had only grown two mil¬ 
limetres, while the same part of the healthy foot had increased 
two and a half millimetres, this was owing to the recovery 
of a somewhat large degree of sensation at this date in the 
neurotomised foot. 
The growth of the horn in length in the neurotomised foot 
had no influence on the thickness of the wall, as when mea¬ 
sured it was found to he the same in both feet. 
From all this it might be concluded, that the growth of the 
horn and hair does not require nervous influence ; for if it 
did, the increase in the hoofs of the neurotomised feet would 
not have taken place ; their length must have remained sta- 
