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HIGHLAND AND AGRICULTURAL SOCIETY. 
and point to its propagation by some common and wide-spread 
cause. Now, the only condition to which all influenza patients of 
every species, country, and time, have been alike exposed, is the 
breathing of the same atmosphere, and hence all investigators, from 
the earliest times, have sought in the atmosphere for the cause of 
influenza, and also, we may add, of all other epidemic and epizootic 
diseases. Before much was known of the atmosphere, it was 
thought that the salubrity of different localities depended on the 
amount of oxygen in the air of such localities, and that a high state 
of health and a large proportion of oxygen must ever coexist. But 
such opinions are now quite untenable, for it is well known that 
the composition of the air, as respects its proportion of oxygen, is 
fixed and unvarying in all localities, healthy or unhealthy. Disease 
has sometimes been ascribed to an undue accumulation in the air of 
the poisonous carbonic acid gas ; but, unfortunately, for the credit 
of this opinion, no such accumulations of carbonic acid are ever 
found to prevail over any great extent of country, or to coexist 
with the occurrence of any epidemic or epizootic disease. Dr. Prout 
and others have believed influenza to depend on the presence in the 
air of sileuiuretted hydrogen ; but this gas, though acrid and irri- 
tating, is very easily decomposed by oxygen, and hence cannot 
exist free in the air, while the products of its decomposition are 
quite innocuous. It was, at one time, believed that various epidemic 
and epizootic diseases were capable of being produced by sulphu- 
retted hydrogen — a theory first propounded by Professor Daniel, of 
King’s College, London, as especially elucidating the development 
of the destructive fevers which occur on the African coasts. The 
insufficiency of this theory was but too well shown in the disastrous 
fate of the Niger expedition, which left this country in 1841, and 
which suffered most severely from fever, though special precautions 
had been made for purifying the air breathed by the crews, especially 
while below decks. Were sulphuretted hydrogen the active exciting 
cause of influenza or any other disease, we should certainly expect 
such disease to be especially prevalent among those most exposed to 
the breathing of the gas. Many chemists spend half their lives in 
an atmosphere containing it in quantities often large and unplea- 
santly sensible to those unaccustomed to the odours of a laboratory; 
and the people employed at gas manufactories, and in various sorts 
of chemical works, breathe it constantly, and often in considerable 
amount. Yet none of these persons are especially liable to influenza, 
but are, on the contrary, remarkably free from all kinds of illness ; 
and hence, we are surely warranted in concluding that sulphuretted 
hydrogen cannot be the cause of influenza. Influenza, like various 
other diseases, has been ascribed to the undue quantity in the air of 
a peculiar principle called ozone, discovered by Professor Schonbein, 
and believed to be an allotropic modification of oxygen, an oxide of 
hydrogen, or, according to Mr. Stevenson Macadam, an oxide of 
nitrogen. But though there is little doubt that a substance such as 
ozone does exist in the air, there is no evidence to prove that its 
presence has anything to do with the production of influenza. On 
