ON THIS EXTERNAL CAUSES OF DISEASE. 217 
reduce the increased action at an early period, the disease sub¬ 
sides ; whilst in the malignant epidemic, after the excitement is 
reduced, the greatest danger is still behind. It is, in fact, a dis¬ 
ease of that mysterious fluid which, in health, gives life and 
nourishment to every solid of the system; and which, when 
vitiated, is by far the most frequent cause of death. 
Having now (at least we hope so) brought forward sufficient 
proof to substantiate our first position ,—that in diseases arising 
from aerial poison, the blood is vitiated ,—we shall proceed to in¬ 
quire into the principal sources of aerial poisons. 
We have already stated, that we have no test of their pre¬ 
sence beyond their effects; and what the precise nature of this 
deleterious principle is, we are altogether unacquainted with; but 
if it were in our power to behold the constitution of the atmo¬ 
sphere with our bodily, as with our mental eyes, we should then 
view the fertile sources of fevers, whatever their form, type, or 
appellation, and of many diseases incident to both men and 
animals, the nature and origin of which we are little acquainted 
with, though their effects are very conspicuous. Such a view 
would explain what Hippocrates long since called the to 0uo», 
or something divine or inexplicable. For into the circumambient 
air, as it is called by Lucretius, we should see carried up what¬ 
ever exhalations arise, not only from the earth itself, but from 
every organized form of matter, whether living or in a state of 
decomposition, that is found upon the surface of the earth : the 
dews of morning, the balm of evening, the fragrance of flowers, 
the breath and characteristic odour of every animal, the vapour 
invisibly arising from the whole ocean and its tributary streams, 
and lastly, that circumscribed and baneful effluvia, however gene¬ 
rated, which, when confined to definite portions of the atmo¬ 
sphere, produce those various forms of disease that infect par¬ 
ticular places. 
Were it possible to obtain such a view as we have imagined, 
the gases arising from an ill-ventilated and crowded stable 
would probably assume the most heterogeneous appearance, as 
we know it to be the most vitiated. Any person may be satisfied 
of this, by visiting one of those hot and pestilential stables of a 
morning, when the infected breath of the crowded inmates be¬ 
comes a putrid exhalation, which trickles down its walls; and 
where the atmosphere reeks with the effluvia of filth and 
wretchedness. 
“ It is not air 
That from such a source reeks back to thine, 
Sated with exhalations rank and fell, 
The spoil of dunghills, and the putrid thaw 
Of nature,— when from shape and texture she 
Kclapscs into fighting elements.” 
