it any longer. No negative facts, no opposing opinions, be they
what they may, or whose they may, can form any answer to the
series of cases now within the reach of all who choose to explore
the records of medical science.

If there are some who conceive that any important end would be
answered by recording such opinions, or by collecting the history
of all the cases they could find in which no evidence of the
influence of contagion existed, I believe they are in error.
Suppose a few writers of authority can be found to profess a
disbelief in contagion,--and they are very few compared with
those who think differently,--is it quite clear that they formed
their opinions on a view of all the facts, or is it not apparent
that they relied mostly on their own solitary experience? Still
further, of those whose names are quoted, is it not true that
scarcely a single one could, by any possibility, have known the
half or the tenth of the facts bearing on the subject which have
reached such a frightful amount within the last few years? Again,
as to the utility of negative facts, as we may briefly call
them,--instances, namely, in which exposure has not been followed
by disease,--although, like other truths, they may be worth
knowing, I do not see that they are like to shed any important
light upon the subject before us. Every such instance requires a
good deal of circumstantial explanation before it can be
accepted. It is not enough that a practitioner should have had a
single case of puerperal fever not followed by others. It must be
known whether he attended others while this case was in progress,
whether he went directly from one chamber to others, whether he
took any, and what, precautions. It is important to know that
several women were exposed to infection derived from the patient,