vaccination.

The influence of previous vaccination often scarcely shows itself in the
stage which precedes the appearance of the eruption of small-pox, the
fever being often just as intense, and the general symptoms just as
severe as in the unmodified disease. The difference, however, becomes at
once obvious with the appearance of the rash. The pocks are always much
fewer than even in mild small-pox, sometimes even not more than twenty.
They never attain above half the size of the ordinary small-pox
pustules; they run their course and dry off in half the time, and
consequently the dangerous fever which accompanies their development in
the natural disease is almost or altogether absent in the vast majority
of instances.

If vaccination did no more than this it would be hard to overestimate
its value, or to praise as it deserves the merit of its discoverer.

=Chicken-Pox= is an ailment of such slight importance that it would
scarcely call for notice if it were not that the resemblance of the
eruption to that of small-pox sometimes leads to its being mistaken for
that disease.

It is highly contagious, and for this reason perhaps it is usually met
with in infancy and early childhood. Sometimes, though by no means
constantly, the eruption is preceded for twenty-four or thirty-six hours
by slight feverishness; but oftener the appearance of the rash is the
first indication of anything being the matter. It shows itself in the
form of small pimples, which in a few hours change into small circular
pocks containing a little slightly turbid fluid. They appear on the
forehead, face, and body, but very rarely on the limbs; they enlarge for
some two or at most three days, then shrivel and dry up; and at the end
of a week the crusts or scabs fall off, scarcely ever causing any
permanent pitting of the skin. They are usually not above twenty or
thirty in number, though every now and then they are much more numerous
without any obvious reason. Their distinction from the small-pox
eruption consists not only in the smaller size of the pocks, and in the
entirely different course which they run, but also in the fact that two
or three successive crops of the eruption appear in the course of five
or six days, so that new ones, those at maturity, and those on which the
crusts have already formed, or from which they have already fallen, may
be seen on the child at the same time. This is sufficient of itself to
establish the difference betw