LIVERPOOL VETERINARY MEDICAL ASSOCIATION. 
557 
the stimulus of either volition or reflex impressions, but also serves 
to co-ordinate the action of any special set of muscles which are 
to determine the performance of any specific act. The correctness 
of this assumption is also supported by the fact that the spasm 
frequently diminishes in violence after several flexions of the limb 
have been made, for it would appear that these preternaturally ex¬ 
cited nerve-cells after a period of repose have a superabundance of 
motor power, as it were, stored up in them, or, in other words, rest 
renders them more irritable ; but after the increased irritability has 
been in a manner discharged in the production of a succession of 
inordinate contractions, ordinary stimulation only produces normal 
action, until a further period of rest or undue stimulation has 
again rendered the cells abnormally excitable. 
There is still another possible cause of the spasm of stringhalt, 
namely, an absence or, more correctly, a tardiness of action in the 
nervous structures which supply the muscles engaged in extending 
the hock and limb in a backward direction, those whose function is 
immediatelv antagonistic to the muscles in which the undue con- 
traction takes place. 
The exceptional conformation of the tibio-astragalean articula¬ 
tion, and the relation of the muscles controlling the action of the 
joint, considerably favour this theory. In bending the hock of a 
dead subject little manipulation is required to check undue flexion 
until a certain point is reached, which point I believe marks the 
limit of natural and ordinary movement; but if continued beyond 
this it will be found that considerable effort is necessary to prevent 
the extreme flexion of which the joint is capable from taking place. 
In ordinary natural movement of the hind leg acute flexion of the 
hock-joint never takes place, but in accordance with nature’s pre¬ 
ordained plan the whole action is regulated both in regard to time 
and degree by the special control of the spinal cord, so that the 
extensor muscles are called into play before their antagonists have 
bent the hock beyond the point of limit before alluded to, and, 
being possessed of greater power, in the first place counteract undue 
flexion, then bring down the foot, straighten the hock, and, finally, 
extend the limb backwards. This much seems to me evident, be it 
from whatever primary cause it may—that if the extensor muscles 
of the hock are inert or slow to counteract the action of the flexors, 
undue contraction of the latter would determine acute flexion of 
the joint, accomplished with a jerk simulating or identical with the 
spasm of stringhalt. 
SHIVERING. 
Shivering, so far as I am aware, only attacks draught horses ; it 
is nofcongenital, but is hereditary to a very high degree, more espe¬ 
cially" from the sire. I have never seen it manifested before the 
colt has been yoked, and believe it is usually developed after the 
horse has been worked for.some time, but it frequently does not 
appear until the horse becomes somewhat advanced in age. All of 
you are acquainted with the symptoms presented by a shiverer; I 
may merely state that they vary in degree from only slight and 
