arty,
should be vaccinated when a month or six weeks old. Rarely or never
ought it to be delayed beyond two or three months. This early period of
life is also particularly suitable to vaccination, because the
accompanying fever will then be over before the disturbing influence of
teething begins.

RE-VACCINATION.

If the first vaccination be found imperfect in character, that is, if it
has not properly 'taken,' the operation should be repeated at the
earliest opportunity. It has been recommended, in all cases, to perform
a second vaccination not later than the sixth or eighth year. If
small-pox be prevailing, it is proper to vaccinate all who have not been
vaccinated within three or four years. In any event, re-vaccination at
or after the period of puberty is of extreme importance. It will give
additional security even to those whose original vaccination was
perfect. In some cases, the susceptibility to small-pox is not wholly
exhausted by one vaccination. Inasmuch as it is desirable for every one
to escape this disease, even in its most modified form, re-vaccination
should always be performed, as it affords a very sure and trustworthy
means of such escape. After successful re-vaccination, small-pox, even
in its mildest shape, is rarely met with. In girls especially, in whom
the changes which occur at puberty are most marked, re-vaccination
should be performed about the age of fourteen.

GROWTH AND DEVELOPMENT.

During infancy the body grows with great rapidity. About the end of the
third year one-half of the adult height of the body is attained. After
this period growth is more gradual; for in order to reach the remaining
half, about eighteen years more are required. At twenty years of age the
height is somewhat more than three and a half times that at birth, and
the weight about twenty times. Development does not go on at an equal
rate in all parts of the body. The lower limbs, small at birth, increase
proportionally more rapidly, while the head, relatively large at birth,
developes more slowly. The muscular system is gradually strengthened. At
the end of the third month the infant is able, if in good health,
readily to support its head; at the fourth month it can be held upright;
at the ninth month it crawls about the floor; by the end of the year it
is able with assistance to step; and between one and two years, at
different times, according to its vigor and activity, it acquires the
power of standing and w