RESPIRATION. 
377 
tion. The first alteration in an atrophied muscle is a diminution 
of the volume of blood supplied to it — next a paleness of colour 
consequent on the loss of blood. As the change advances, the dis- 
organization increases, the bulk diminishes, and may proceed to 
an entire loss of the part ; but, more commonly, this state is much 
modified. Hypertrophy of the muscles commonly arises from in- 
creased action or function, which is to be considered purely phy- 
siological : thus the loss of action in one set of muscles occasions 
increase of function in others. The muscles in the arms of a black- 
smith are strongly formed, while those of his lower extremities 
are imperfectly developed, from the standing behind the anvil 
limiting their action. But this solution of the phenomena in the 
above muscles does not aptly apply to the change in the muscles 
of the larynx ; the direct stimulus of exertion is continued on the 
one hand, while that of organic function is the influence on the 
other. Obliteration of the nervous current in one branch gives 
rise to increased power in that of the opposite nerve, in the same 
manner as the loss of an arterial trunk gives rise to enlargement 
of the collateral vessels. 
The earliest and most essential change in a muscle or part that 
is hypertrophied is an obviously excited or augmented organic 
nervous influence. Powerful muscular contraction and increased 
vascular determination are produced by it ; and excess of the nu- 
tritient principle and increase of bulk is the general result. 
It is necessary to hypertrophy that the distribution of blood to 
the part should be augmented, and that the nutritive molecules 
be superabundant ; but this state of the parts is dependent upon 
the excess of organic nervous power. The same states of vital 
attraction and power of affinity extend to the muco-membra- 
nous and submucous tissues; and this condition may occur in 
those structures, independent of topical inflammation. When 
the distribution and function of the par-vagum, or, as Mr. Youatt 
very properly defines it, “ cerebro-visceral motor nerve,” is viewed 
throughout all its relations, it is easy to conceive the origin of 
these forms of lesion obtaining in the different tissues consti- 
tuting the larynx, to be frequently seated in the digestive and 
assimilating organs ; arising out of a species of gastro-enteric 
irritation with hepatic disorder, commonly produced or esta- 
blished by unwholesome and injudicious feeding; and by exer- 
tions of the animal during those states of surcharge of the abdo- 
minal viscera — unequal exertions to which the horse, of all other 
animals, is so frequently subjected. The intensity of the irrita- 
tion alluded to is not of that high grade as to manifest its exist- 
ence by signs of acute suffering: notwithstanding, however, that 
horses do endure a very great deal of inward pain without por- 
