r on the face may not occur until several years later. I
remember also that I have seen boys in whom during the period of puberal
development an enlargement of the mammae took place, going so far that it
was possible by pressure on the glands to expel fluid from the
mammillary ducts; at a more advanced age, however, this mammary growth
was arrested, and subsequently atrophy ensued.

But all these observations notwithstanding, the fact remains well
established that even in childhood notable sexual differences make their
appearance. Other observations, too, confirm this notion of sexual
differentiation--for example, pathological experiences.

There are some diseases to which women are especially liable, others
which occur by preference in men. To some extent, indeed, this is
explained by the special exposure of one sex or the other to certain
noxious influences. The neuroses that appear as the sequelae of injuries
are especially common in the male sex, because the occupations of men
expose them more than women to injuries of all kinds. Of such cases, of
course, we do not speak here. But there are some unquestionably
hereditary morbid tendencies which manifest themselves by preference in
one sex or the other, and such sexual predisposition shows itself even
in childhood. I propose to give instances of this; some quoted from
Moebius,[18] some from other authors, and some taken from my own personal
experience.

Chlorosis is a disease of feminine youth, but very often makes its
appearance in childhood, especially towards the end of the second period
of childhood, at this earlier age, also, attacking girls in preference
to boys. Haemophilia, on the other hand, and also certain hereditary
forms of muscular atrophy, occur chiefly in males, and this in early
childhood. Diabetes is principally a disease of adults, but occasionally
it is met with in children also; among adults, there is a considerable
preponderance of males affected with this disease when diabetes occurs
in childhood, the disease also exhibits a preference for the male sex,
although at this time the peculiar sex-incidence is less marked than in
later life. Congenital defects of the heart are commoner in boys, the
proportion obtained from a very large number of cases of this kind being
61.6 boys: 38.4 girls. Chorea (St. Vitus's dance) affects girls more
often than boys, the ratio in this case being 2.5 girls: 1 boy. In the
case of whooping cough, we find that two