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 and
destruction of the fluids of the animal body, set up by minute organisms
which are the cause of this destruction and of this disturbance; and
only recently the study of the phenomena which accompany vaccination
has thrown an immense light in this direction, tending to show by
experiments of the same general character as that to which I referred as
performed by Helmholz, that there is a most astonishing analogy between
the contagion of that healing disease and the contagion of destructive
diseases. For it has been made out quite clearly, by investigations
carried on in France and in this country, that the only part of the
vaccine matter which is contagious, which is capable of carrying on its
influence in the organism of the child who is vaccinated, is the solid
particles and not the fluid. By experiments of the most ingenious kind,
the solid parts have been separated from the fluid parts, and it has
then been discovered that you may vaccinate a child as much as you like
with the fluid parts, but no effect takes place, though an excessively
small portion of the solid particles, the most minute that can be
separated, is amply sufficient to give rise to all