378 ON THI2 EXTERNAL CAUSES OF DISEASE, 
In many instances nature tempers the high degree of heat 
belonging to particular climates by the periodical recurrence of 
cooling winds at stated hours of the day; and the alternations of 
a pale blue colour. It was thickest at noon, when the sun appeared through 
it of a red colour. Rain did not, in the least degree, affect it. This haze 
is said to have possessed drying properties, and to have occasionally yielded 
a strong and peculiar odour. It is also said to have deposited in some 
places a viscid liquid, of an acrid taste and of an unpleasant smell. 
“ The dispersion of this haze in 1783 was attended by severe thunder 
storms. As might be expected, the general state of health has, for the 
most part, been deranged during the continuation of these phenomena. 
Simultaneously, there have been epidemic diseases of various kinds. Thus, 
in the above-mentioned years, 1782 and 1783, an epidemic catarrh, or in¬ 
fluenza, prevailed throughout Europe; affecting not only mankind, but 
likewise other animals.” 
This remark of the learned doctor coincides w ith those of our friend Mr. 
Youatt, in his lectures delivered at the University of London, who has 
given a very interesting account of the epidemic that prevailed among 
horses, in the year 1783, throughout all Europe*. 
The nature of the matter thus diffused through the atmosphere is quite 
unknow n. It may be as various at different times as the character of the 
epidemics to which it gives origin. “ As an example of the extraordinary 
effects which foreign bodies, when diffused through the atmosphere, are 
capable of producing, we may mention,” says Dr. Prout, “ those produced 
by sil'enium when in combination with hydrogen, it is diffused as a gas 
through the air, even in the most minute quantity. The effects of this 
gaseous combination of silenium with hydrogen are thus described by the 
celebrated chemist Berzelius, its discoverer. ‘ In the first experiment 
which I made on the inhalation of the gas, I conceive that I letup into 
my nostrils a bubble of gas, about the size of a small pea ; it deprived me 
so completely of the sense of smell, that I could apply a bottle of concen¬ 
trated ammonia to my nose without perceiving any odour/ On another 
occasion, while preparing the gas, Berzelius felt at first a sharp sensation 
in his nose ; his eyes then became red, and other symptoms of catarrh be¬ 
gan to appear. In half an hour, he w as seized with a dry and painful 
cough, which continued for a long time, and which was, at last, accompa¬ 
nied by an expectoration, having a taste entirely like that of the vapour 
from a boiling solution of corrosive sublimate. These symptoms were, at 
length, removed by the application of a blister to his chest/’ 
Dr. Prout does not tell us that this gas is actually diffused through the 
atmosphere during the prevalence of epidemic disease ; but as silenium, 
like sulphur, is a volcanic product, such a substance, being ejected from 
the crater of a volcano during an eruption, or through a crevice in the 
earth during an earthquake, may thus produce an epidemic disease. His 
intention is merely to shew, that a small quantity of an active ingredient, 
like silenium, is sufficient to contaminate the atmosphere over a wide ex¬ 
tent of country. 
“The matters,” says the doctor, “occasionally diffused through the at¬ 
mosphere, which appear to be in a state of solution , are not often percept 
tible by our senses, unless in some cases, perhaps, by the sense of smell.” 
As an instance of the presence of such bodies in the atmosphere, he 
* See Thl Veterinarian, vol. vi. 
