vident and no less interesting.

The Genital System.

a. =Structural Changes.=--The external genitals, besides showing the
pudendal pilosity referred to above, are all greatly increased in
size. The penis is increased in all of its dimensions, the testes
become very much increased in size, the scrotum, probably because of
the increased weight of the testes, is also lengthened.

b. =Functional Changes.=--The testes and associated glandular bodies
gradually develop the power of forming perfect semen, capable of
fertilizing the human ovum. When these organs thus become capable of
procreation, the period of puberty is complete.

In this connection it is important to note that the development of the
testes produces a profound effect upon both the physical and mental
characteristics of the young man. This effect is produced through a
substance formed in the testes and reabsorbed into the body, thus
gaining access to the blood where it exerts its mysterious but
profound influence. Just how this affects the mind and body will be
discussed in detail in a subsequent chapter.

2. PSYCHICAL CHANGES.

Play and Work.

a. =Sports.=--Most of the higher animals, particularly man, and all
races of men, devote a large part of the energies of the adolescent
period to sports or games in which individuals contend with each other
or teams of individuals contend with opposing teams in games that
bring into play the various powers of the neuro-muscular system: such
as alertness of all the senses, readiness and correctness of judgment,
agility, speed and strength of movement. Sports might be criticised by
some because they represent non-productive expenditure of energy. On
the other hand, no energy ever expended by man is so highly productive
of so precious a material as results from manly athletic sports. The
products of these games are the substances consumed by them,
paradoxical as that may at first appear. The use of brain, muscle and
glands and the consumption of the cell substances of these tissues
results in the development of the nerve, muscle and gland cells into
a condition larger, better equipped and more responsive than before
such use.

Thus, athletic sports, while they make draughts upon the nerves,
muscles and glands, develop all of these tissues to a high degree of
efficiency. The plan of nature in this instinctive indulgence in
sports must be evident. Nature is educating and developing the male
animal (man) to the