of the fifteenth year as the termination of childhood, we may
divide childhood into two equal periods, the first extending from birth
to the completion of the seventh year, the second from the beginning of
the eighth to the end of the fourteenth year. I shall in this work
designate these two periods as the _first_ and the _second period of
childhood_ respectively. In the first period of childhood, the first
year of life may be further distinguished as the _period of infancy_.[1]
The first and second periods of childhood comprise childhood in the
narrower sense of the term. The years that immediately follow the
beginning of the fifteenth year I shall denote as the _period of youth_.
Inasmuch as the symptoms of this latter come to differ from those of
childhood proper, not abruptly, but gradually, the first years, at
least, of youth will often come under our consideration, and I shall
speak of this period of life as the _third period of childhood_.
Although childhood in the narrower sense comprises the first and second
periods only, childhood in the wider sense includes also the third
period. It is hardly possible that any misunderstanding can arise if the
reader will bear in mind that whenever I speak of childhood without
qualification, I allude only to the period of life before the beginning
of the fifteenth year. For all these periods of childhood, first,
second, and third, I shall for practical convenience when speaking of
males use the word _boy_, and when speaking of females, the word _girl_.

The use of this terminology must not be regarded as implying that the
distinctions indicated correspond in any way to fixed natural lines of
demarcation; on the contrary, individual variations are numerous and
manifold. Not only does the rate of development differ in different
races (in the Caucasian race, more especially, the age of puberty comes
comparatively late, so that among the members of this race childhood is
prolonged); but further, within the limits of one and the same race,
notable differences occur. More than all have we to take into account
the differences between the sexes, childhood terminating earlier in the
female sex than in the male--among our own people [the Germans] this
difference is commonly estimated at as much as two years. In addition,
in this respect, there are marked differences between different classes
of the population, a matter to which we shall return in Chapter VI.

It is also necessary to po