the three-thousandth of an inch in diameter--not bigger than one of
those little coloured specks of matter in my own blood at this moment,
the weight of which it would be difficult to express in the fraction of
a grain--and put it into this solution. From that single one, if the
solution were kept at a fair temperature in a warm summer's day, there
would be generated, in the course of a week, enough torulae to form a
scum at the top and to form lees at the bottom, and to change the
perfectly tasteless and entirely harmless fluid, syrup, into a solution
impregnated with the poisonous gas carbonic acid, impregnated with the
poisonous substance alcohol; and that, in virtue of the changes worked
upon the sugar by the vital activity of these infinitesimally small
plants. Now you see that this is a case of infection. And from the
time that the phenomenon of fermentation were first carefully studied,
it has constantly been suggested to the minds of thoughtful physicians
that there was a something astoundingly similar between this phenomena
of the propagation of fermentation by infection and contagion, and the
phenomena of the propagation of diseases by infection and contagion.
Out of this suggestion has grown that remarkable theory of many
diseases which has been called the "germ theory of disease," the idea,
in fact, that we owe a great many diseases to particles having a
certain life of their own, and which are capable of being transmitted
from one living being to another, exactly as the yeast plant is capable
of being transmitted from one tumbler of saccharine substance to
another. And that is a perfectly tenable hypothesis, one which in the
present state of medicine ought to be absolutely exhausted and shown not
to be true, until we take to others which have less analogy in their
favour. And there are some diseases most assuredly in which it turns
out to be perfectly correct. There are some forms of what are called
malignant carbuncle which have been shown to be actually effected by a
sort of fermentation, if I may use the phrase, by a sort of disturbance