Let it be supposed that there is prevailing, in a district of country, disease to a great amount, that is to say, many cases of the same distemper.
That single circumstance proves nothing in reference to atmospheric contagion, more than to any other probable cause of disease. It shews, merely, that there is in wide operation some cause or causes of sickness; and it is totally unwarrantable to conclude that one agency, more than another, is the efficient cause, without further information directly bearing on the subject.
It is with the knowledge of the single fact, and in total ignorance of others, or with total blindness to them, that atmospheric contagion is pronounced to be the active agent.
Now it is not the peculiar property, the exclusive prerogative of that principle, to cause disease; at least, that character has not been openly sought by its advocates, though the tone of common conversation, and of medical writings on the subject, would seem to imply that it had been tacitly granted.
That cannot be conceded. Many other agencies are known to be productive of sickness, and have, on many occasions, induced pestilence of a deadly character, that has ravaged in no despicable limits.
The isolated fact itself of disease being widely extended in the absence of particulars, after proving that some cause existed, should legitimately go to create a suspicion, that the cause or causes which had produced the first cases, and acted as the ordinary springs of the malady, were continuing to operate on other individuals. Such would be known to be capable of producing the effect observed, for the satisfactory reason, that it or they had already accomplished it. How much more wise, under such circumstances, it would be to suspect the continuance of that influence with the continuance of effects identically the same as it or they had already produced, than to call in a principle whose only evidence of existence was the presence of effects, the same as had been only a short time before produced by a different agency, and of whose removal or absence there was not a particle of proof.
But a little inquiry will, on most occasions, elicit the fact, that some pestiferous influences exist; and it will, in general, be soon enough to pronounce on the probable causes of a distemper after that investigation has been made.
Disease in general, unconnected with alterations in the texture of the organs, is neither more nor less than a derangement of the functions performed by the body; and as it partakes of a general or local character, so the disease is either local or general; and, as it relates to functions, more or less important, so it is more or less dangerous.
It must be obvious, that a machine so nicely balanced, so complicated and so exquisitely wrought as the human body, must be liable, on many occasions, to have its operations impeded and deranged; and, although sometimes said to be a little world of itself, still, it is dependent on surrounding agencies. It requires a pure atmosphere for respiration, food to supply the waste it continually suffers, and drink to appease thirst, and to take the place of the fluids that are constantly draining from it.
The human body is necessarily brought in contact with the external world; and many are the injuries it suffers therefrom, both directly and remotely.