pated.

These anticipations have not hitherto been fully realised; but the good
effected by vaccination has been such as to render it, in the opinion of
nearly everyone qualified to form an opinion on the subject, one of the
greatest boons ever conferred on the human race.

Small-pox, like other eruptive fevers, has the peculiarity of occurring
for the most part only once in a person's life. We do not know in the
least on what this protecting influence depends. We know the fact, but
are the less able to offer an explanation, since there are other
constitutional diseases, such as gout and rheumatism, in which the local
symptoms are equally the outcome of previous constitutional disorder,
where exactly the opposite rule obtains, and in which their occurrence
does but increase the liability to their return.

The protective power is apparently possessed by the mild form of the
disease communicated by inoculation as much as by the severer form of
small-pox which is contracted by direct contagion or infection. This
knowledge has been applied in the treatment of some of the diseases of
animals, and it has been found in the case of the so-called small-pox in
sheep (a disease which, however, is quite distinct from human small-pox)
that while one in two of the animals who contracted it in the ordinary
way died, death took place in only three per cent, or not one in thirty,
of those in whom it was produced by inoculation; and the inoculated
sheep were thereby safeguarded from subsequent attacks as completely as
the others.

This knowledge was more recently applied by the distinguished Frenchman
whom I have already mentioned, M. Pasteur, in the case of a fatal
pestilence among sheep in many parts of France, known by the name of
_charbon_. The inoculated sheep died, however, in such large numbers,
though in a somewhat smaller proportion than those who had been directly
infected, that he found it necessary to weaken the matter which he
employed by admixture with other innocuous materials. This experiment,
however, again yielded unsatisfactory results; slight symptoms of the
disease were produced, but the protection thus afforded was inadequate
and uncertain. Some few resisted the disease, but others contracted it
and died. With that clear insight which constitutes genius, M. Pasteur
next tried the experiment of inoculating the sheep first with a weak
matter which produced but slight symptoms, but at the same time enabled
the anim