224 ON CHOLERA IN DOMESTICATED ANIMALS. 
illustrate by the effects of the movement of the jaws in bleeding 
from the neck of the horse, the blood is driven with increased 
force from the veins of the muscle and from the neighbouring 
parts, in consequence of the contraction of the muscle. That 
contraction, if continued, also resists the entrance of the blood 
into the arteries of the parts in action, and compressed. That 
bloodvessels are liable to be acted upon by pressure, I need not 
attempt farther to prove; but the example of the horse’s foot, 
however, is not unw’orthy of notice: there we find the arteries 
passing through the bone, that pressure may not affect them; 
and that the veins may not be injured by it, we find them anasto¬ 
mosing like a piece of net-work, and without valves, in order 
that the blood may escape from them in every direction, while 
under its influence. 
From this cause, then, we have an absence of blood, or, 
perhaps, it may be, a little extravasation, in the capillaries; and 
this resistance to the free circulation acts on the heart, and 
impedes its action, and also compels the blood to flow to those 
parts which are not subject to pressure. This accounts for 
the congested state of the vessels of the brain and spinal 
cord—an appearance which is to be found as an effect of all 
spasmodic affections, more especially in tetanus; and an effect 
that has frequently been mistaken for the cause of that disease. 
From the same cause we find the vessels of the abdomen in a 
state of congestion. The lungs also, and the heart, and large 
vessels of the chest, are liable to be conorested in a similar 
This production of congestion in the vessels of the important 
oro^ans enables us to account also for the occurrence of the fever 
which so frequently follows the other more active symptoms. 
The congestion of the vessels of the brain and spinal cord may 
be naturally expected to produce some derangement in these 
organs; hence headach in the mildest, but typhous fever in the 
more severe cases, the consequence of recovery from the first 
shock of the disease. 
These effects of the disease upon the nervous system in my 
natients I have not observed, unless I w^ere to refer the dulness 
which sometimes exists for a few days to this cause ; or, to sup¬ 
pose that some of these cases, where the disease affects the 
mucous membrane of the bronchi®, and which are ushered in 
by colicky pains, are cholera ; but this I do not feel disposed to 
do, nor is it, I think, of much importance that t should en¬ 
deavour to trace the analogy so far. I shall keep this in view, 
should any well-marked case occur. 
It is now necessary that I should offer some reason why the 
