ON THE EXTERNAL CAUSES OF DISEASE. 219 
the most common and fatal (though slow) diseases to which 
horses are liable. In the mucous membranes it produces catarrh, 
thick wind, chronic cough, sore throat, roaring, wheezing, 
whistling, dysentery. See. &c. In the cellular structures it pro¬ 
duces tliose anasarcal deposits, such as dropsy of the skin, swell¬ 
ed legs. Sec. It disposes the skin to various complaints, such as 
man° e, grease, Sec .\ and, as an appendix to tne frightful catalogue, 
we may add, farcy, glanders, and that cuise on good horse-flesh, 
specific ophthalmia. 
We beg to remark, en passant , that we do not suppose that 
in every one of the diseases we have mentioned as pioduced by 
breathing a poisioned atmosphere, the blood is diseased. It 
would be very unphilosophical, for instance, to suppose that 
m roaring, whistling, thick wind, or chionic cough, the bloou is 
contaminated. In these cases, aerial poisons probably act as 
chemical or mechanical stimuli to the mucous membrane which 
lines the air-passages. 
The limits of this paper will prevent our entering so minutely 
into the subject as we might wish. It is extremely probable 
that the qualities of the blood are considerably altered in many 
diseases, though such changes cannot oe detected. We obsei\e, 
for example, a complete alteration in the seium in jaundice in 
the human subject j and were it not for that cnange of colour, we 
should, perhaps, have no evidence that the blood was at all al¬ 
tered in ‘that disease. Velpean* has lately published a Memoir, 
wherein he observes how much the humoial pathology has been 
neglected, and of what great importance it is to become ac¬ 
quainted with the morbid changes that take place in the blood j 
and to illustrate this remark, he details some cases, wherein pu - 
riform matter was found floating in, and mixed with, the general 
mass of blood throughout the different large vessels, both arte¬ 
ries and veins. In these cases, abscesses in great numbeis, though 
unaccompanied by the usual characters of inflammation, were 
found in various parts. 
The next point that requires our attention will be, the means 
we possess for the correction of the evils hinted at. That c pre¬ 
vention is better than cure,’ 5 is a maxim, the truth of which is 
universally admitted ; and this is not only of importance in respect 
to horses, but to the health of mankind generally, and particulaily 
those inhabiting large towns, as the continual breathing a foul and 
kind, the animal expresses little pain. We have oftentimes seen the com¬ 
plaint accompany disease of the lungs, and those of the ail-passages. Bleed¬ 
ing in the complaint sometimes produces ruptui e of the livei ,and consequent¬ 
ly internal haemorrhage and death, and, in evevy instance, it accelerates the 
catastrophe. 
* Lancet.—Lectures on Surgery, by Mr. War drop. 
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