HIGHLAND AND AGRICULTURAL SOCIETY. 
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state of molecular disturbance or decay, produce serious derauge- 
ment when introduced into the system. We cannot dismiss the 
exciting causes of influenza, without noticing the much- vexed ques- 
tion of contagion. Many facts are adduced in favour of the 
contagious nature of the disorder. It is said, for example, that it 
spreads chiefly to those places which have had communication with 
others previously invaded by the disease ; that the crews of vessels 
at sea have remained free of it until they entered ports where it had 
already existed; that the epidemic of 1803 was introduced into 
Dublin by some packages of goods from an infected part of England. 
On the other hand, however, there is ample evidence to show that 
in many cases the disease does occur independently of contagion. 
Thus, it does not generally present itself in unusually large propor- 
tions among those persons or animals that have had most commu- 
nication with those first affected. It often attacks one or two horses 
standing in different parts of a large stable without spreading 
to the others, and sometimes attacks only one animal of a 
team. It often springs up at the same time in several different 
places widely removed from each other. The epidemic of 1836 
occurred at the same time in London and at Cape Town. In May, 
1782, while influenza was prevailing in different parts of England, 
the late Admiral Kempenfelt’s crew became affected by it after they 
had been nearly a month at sea, and at the same time Lord Howe’s 
fleet, then cruising in the channel, was also affected . — ( Annals of 
Influenza , op. cit.) But these statements, apparently so contra- 
dictory and inconsistent, may be to a great extent harmonised, if it 
be recollected that there is probably no distinct line of demarcation 
between contagious and non-contagious maladies, and that the same 
disease may be developed, sometimes through the intervention 
of contagion, and sometimes independently of it. Cholera in 
man, glanders in the horse, pleuro-pneumonia in cattle, and 
the eruptive fevers in all animals, afford good illustrations of 
this. The difference betwixt a disease being contagious and 
non-contagious merely resolves itself into a question as to the 
source of the disease-producing poison, which is derived in the 
former case from some concatenation of external circumstances 
generally obscure and unknown, and in the latter either directly or 
indirectly from the body of an animal already affected by the 
disease. Now, as respects influenza, the orgairic germs, which we 
shall for the present consider as the immediate cause of the disease, 
are in the great majority of cases produced by causes of which we 
as yet know nothing ; but they may also, we think, be occasionally 
evolved from the bodies of animals affected by the disease. The 
exciting causes of influenza are often of themselves insufficient to 
induce the disease, and usually require the co-operation of certain 
conditions which are termed predisposing causes. These owe 
their effects to their rendering the body unusually susceptible to the 
exciting causes of the disease. They prepare a fitting and con- 
genial soil, as it were, into which the active exciting causes fix 
themselves, and they deserve our careful attention as being more 
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