surely as the fig
comes from the fig, the grape from the grape, the thorn from the
thorn, so surely does the typhoid virus increase and multiply into
typhoid fever, the scarlatina virus into scarlatina, the small-pox
virus into small-pox. What is the conclusion that suggests itself
here? It is this: That the thing which we vaguely call a virus is to
all intents and purposes a seed. Excluding the notion of vitality, in
the whole range of chemical science you cannot point to an action
which illustrates this perfect parallelism with the phenomena of
life--this demonstrated power of self-multiplication and reproduction.
The germ theory alone accounts for the phenomena.

In cases of epidemic disease, it is not on bad air or foul drains that
the attention of the physician of the future will primarily be fixed,
but upon disease germs, which no bad air or foul drains can create,
but which may be pushed by foul air into virulent energy of
reproduction. You may think I am treading on dangerous ground, that I
am putting forth views that may interfere with salutary practice. No
such thing. If you wish to learn the impotence of medical practice in
dealing with contagious diseases, you have only to refer to the
Harveian oration for 1871, by Sir William Gull. Such diseases defy
the physician. They must run their course, and the utmost that can be
done for them is careful nursing. And this, though I do not specially
insist upon it, would favour the idea of their vital origin. For if
the seeds of contagious disease be themselves living things, it may be
difficult to destroy either them or their progeny, without involving
their living habitat in the same destruction.

It has been said, and it is sure to be repeated, that I am quitting my
own metier, in speaking of these things. Not so. I am dealing with
a question on which minds accustomed to weigh the value of
experimental evidence are alone competent to decide, and regarding
which, in its present condition, minds so trained are as capable of
forming an opinion as regarding the phenomena of magnetism or radiant
heat. 'The germ theory of disease,' it has been said, 'appertains to
the biologist and the physician.' Where, I would ask in reply, is the
biologist or physician, whose researches, in connection with this
subject, could for one instant be compared to those of the chemist
Pasteur? It is not the philosophic members of the medical profession
who are dull to the recep