smitted to the unborn child; in certain cases
the disease is transmitted, in others the developing foetus may be so
injured by the toxic products of the disease that various
imperfections of development result, as is shown in deformities, or in
conditions which render the entire organism or individual organs,
particularly the nervous system, more susceptible to injury. Following
the primary localization of the acquired form of the disease, there is
usually secondary localization in the mucous membrane of the mouth,
and the disease may be transmitted by kissing or by the use of
contaminated utensils. The habit of indiscriminate kissing is one
which might with great benefit be given up.

There is definite relation between age and the infectious diseases. In
general, susceptibility is increased in the young; young animals can
be successfully inoculated with diseases to which the adults of the
species are immune, and certain human diseases, such as scarlet fever,
measles and whooping cough, seem to be the prerogatives of the child.
It must be remembered, however, that one attack of these diseases
confers a strong and lasting immunity and children represent a raw
material unprotected by previous disease. Where measles has been
introduced into an island population for the first time, all ages seem
equally susceptible. All ages are equally susceptible to smallpox, and
yet in the general prevalence of the disease in the prevaccination
period it was almost confined to children, the adults being protected
by a previous attack. The habits and environment at different ages
have an influence on the opportunities for infection. There is
comparatively little opportunity for infection during the first year,
in which period the infant is nursed and has a narrow environment
within which infection is easily controlled. With increasing years the
opportunities for infection increase. When the child begins to move
and crawl on hands and knees the hands become contaminated, and the
habit of putting objects handled into the mouth makes infection by
this route possible. Food also becomes more varied, milk forms an
important part of the diet, and we are now appreciating the
possibilities of raw milk in conveying infection. With the enlarging
environment, with the school age bringing greater contact of the child
with others, there come greater opportunities for infection which are
partly offset by the increase in cleanliness. The dangers of infec