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tain by our most scientific tests what it is. The virus is stirred up 
somewhere, floated and diffused in the air, carried by currents to 
considerable distances, retaining its power of destruction all the time. 
Nay, have we not an equally clear example in the deadly poison 
emitted from the leaves and bursting buds of the Upas tree? 
The criminal condemned to death has the chance given him to go 
to the tree and pluck a branch, by covering his entire body with 
varnish, and approaching the tree in the precise line with the wind 
and holding his breath. It is occasionally done in safety, but were he 
to approach it from any other point it is a million to one but that he 
would inhale by the lungs, or absorb by the skin, a fatal dose ! 
Again, during the cattle plague, there are innumerable instances in 
which a healthy stock, separated from a diseased stock by a river, 
and where every possible precaution was constantly taken to pre¬ 
vent anything passing between them that could act as an agency of 
communication, that such healthy stock has kept healthy until a 
change in the wind has brought the contaminated atmosphere across 
the river, and the healthy cows have from that hour become 
affected! I contend that a virulently infected animal, like the Upas 
tree, is a centre from which poisonous emanations are emitted from 
the lungs, and exhalations from the skin permeate and float in the 
air capable of being carried to various distances, and infect other 
herds without any contact whatever. This is the mode by which 
I consider that infectious diseases are communicated ; but time 
will doubtless reveal far more about these things than we know 
at present. An atmosphere surcharged with a morbific miasma 
may not be discernible by the nicest chemical tests, its presence 
is only inferred from its effects upon animal life; whether it be an 
excess or deficiency of oxygen in the atmosphere, an excess or 
deficiency of some of the other constituents we know not; but this 
we know, that there is a connection between the atmospheric air 
and the occurrence of putrefaction. Is not this proved by meat 
becoming almost immediately tainted under certain conditions of 
the air, while the occurrence of putrefaction is attended by the 
development of various low forms of life ? Of this we are certain, 
that the air around us, especially that in damp, dark, ill-ventilated 
places, contains many floating germs of common fungus, possibly 
many germs of infinitesimal life, producing.various forms of disease. 
Whatever it is that excites fermentation and putrefaction, and, at 
the same time gives rise to living forms in an infusion, is either a 
germ, microzymes and sporules of fungi, or matter divided into 
minute solid particles. Professor Tyndal has most clearly demon¬ 
strated it by this mode : if a fluid eminently fit for the development 
of the lowest forms of life, but which fluid contains no germs at 
the time, be exposed for a short period to the action of ordinary 
air, it gives rise to living things in great abundance ; whilst, on the 
other hand, the same fluid if exposed ever so long to air which has 
been mechanically freed from these germs or solid particles, there 
shall be no such development of life in it. Professor Tyndal has 
thus clearly demonstrated that organic matter, capable of producing 
