that vaccination
does not protect against any other disease than small-pox.

That protection, indeed, is not absolute, nor was the protection
afforded by inoculation absolute; but small-pox after vaccination, even
when it does occur, is very rarely severe, and still more seldom fatal.

There seems good reason for believing that the protecting power of
vaccination tends to diminish with the lapse of time; though apparently
this is not always the case, nor can any direct statement be made as to
the conditions which favour this in one case, or prevent it in another.
As a matter of fact, however, we do know that such a tendency does
exist, and that this tendency calls for the repetition of vaccination
from time to time; such re-vaccination carefully performed being as
nearly as possible an absolute guarantee against small-pox. All persons
engaged as nurses or attendants at the Small-Pox Hospital during the
past thirty-two years, have been vaccinated or re-vaccinated before
entering on their duties, and during this period not a single case of
the disease has occurred among the whole staff. The experience of other
small-pox hospitals for a shorter period is identical. As far as we
know, every seventh year is a reasonable interval at which
re-vaccination should be performed.

One great cause of the failure of the protective power of vaccination
is the unintelligent and careless manner in which it is too often
performed, especially among the poor. To this same cause it is also due
that in some cases of almost infinite rarity one special constitutional
disease has been known to be communicated. I have never seen such a
case, but I know there are such. They are, however, no more a reason
against vaccination than the occasional death from an overdose of opium
is a reason against the use of that drug.

To avoid any risk of this kind, and also with the idea that the power of
the vaccine matter may have become weakened by transmission through many
thousands of persons, vaccination direct from the calf has been
introduced of late years, especially in America and on the Continent.
The time, however, that has as yet elapsed is scarcely sufficient to
test the comparative preservative power of this as compared with
vaccination from the human subject. Its immediate local effects are
somewhat more severe; I do not know any reason why its influence should
not be equally abiding.

There is absolutely no foundation for the idea that scrof