ose in which disease did not
follow exposure,--by the striking example of small-pox, which,
although one of the most contagious of diseases, is subject to the most
remarkable irregularities and seeming caprices in its transmission. It
makes full allowance for other causes besides personal transmission,
especially for epidemic influences. It allows for the possibility
of different modes of conveyance of the destructive principle. It
recognizes and supports the belief that a series of cases may originate
from a single primitive source which affects each new patient in turn;
and especially from cases of Erysipelas. It does not undertake to
discuss the theoretical aspect of the subject; that is a secondary
matter of consideration. Where facts are numerous, and unquestionable,
and unequivocal in their significance, theory must follow them as it
best may, keeping time with their step, and not go before them, marching
to the sound of its own drum and trumpet. Having thus narrowed its area
to a limited practical platform of discussion, a matter of life and
death, and not of phrases or theories, it covers every inch of it with a
mass of evidence which I conceive a Committee of Husbands, who can count
coincidences and draw conclusions as well as a Synod of Accoucheurs,
would justly consider as affording ample reasons for an unceremonious
dismissal of a practitioner (if it is conceivable that such a step could
be waited for), after five or six funerals had marked the path of his
daily visits, while other practitioners were not thus escorted. To the
Profession, therefore, I submit the paper in its original form, and
leave it to take care of itself.

To the MEDICAL STUDENTS, into whose hands this Essay may fall, some
words of introduction may be appropriate, and perhaps, to a small number
of them, necessary. There are some among them who, from youth, or want
of training, are easily bewildered and confused in any conflict of
opinions into which their studies lead them. They are liable to lose
sight of the main question in collateral issues, and to be run away with
by suggestive speculations. They confound belief with evidence, often
trusting the first because it is expressed with energy, and slighting
the latter because it is calm and unimpassioned. They are not satisfied
with proof; they cannot believe a point is settled so long as everybody
is not silenced. They have not learned that error is got out of the
minds that cherish it, a