own as
cancers, the abnormal growth has acquired powers of reproduction and
multiplication, and is only morphologically distinguishable from the
parasitic worm, the life of which is neither more nor less closely bound
up with that of the infested organism.

If there were a kind of diseased structure, the histological elements of
which were capable of maintaining a separate and independent existence
out of the body, it seems to me that the shadowy boundary between morbid
growth and Xenogenesis would be effaced. And I am inclined to think that
the progress of discovery has almost brought us to this point already. I
have been favoured by Mr. Simon with an early copy of the last published
of the valuable "Reports on the Public Health," which, in his capacity of
their medical officer, he annually presents to the Lords of the Privy
Council. The appendix to this report contains an introductory essay "On
the Intimate Pathology of Contagion," by Dr. Burdon-Sanderson, which is
one of the clearest, most comprehensive, and well-reasoned discussions of
a great question which has come under my notice for a long time. I refer
you to it for details and for the authorities for the statements I am
about to make.

You are familiar with what happens in vaccination. A minute cut is made
in the skin, and an infinitesimal quantity of vaccine matter is inserted
into the wound. Within a certain time a vesicle appears in the place of
the wound, and the fluid which distends this vesicle is vaccine matter,
in quantity a hundred or a thousandfold that which was originally
inserted. Now what has taken place in the course of this operation? Has
the vaccine matter, by its irritative property, produced a mere blister,
the fluid of which has the same irritative property? Or does the vaccine
matter contain living particles, which have grown and multiplied where
they have been planted? The observations of M. Chauveau, extended and
confirmed by Dr. Sanderson himself, appear to leave no doubt upon this
head. Experiments, similar in principle to those of Helmholtz on
fermentation and putrefaction, have proved that the active element in the
vaccine lymph is non-diffusible, and consists of minute particles not
exceeding 1/20000th of an inch in diameter, which are made visible in the
lymph by the microscope. Similar experiments have proved that two of the
most destructive of epizootic diseases, sheep-pox and glanders, are also
dependent for their existence and