ou
already know is the sac in which the egg or embryo grows into a baby.
The penis and the vagina are about the same size, as Nature intended
them to fit each other. By a rhythmic movement of the penis in and
out, the sex act reaches an exciting climax or orgasm, when there is
for the woman a peculiarly satisfying contraction of the muscles of
the passage and for the man, the expulsion of the semen, the liquid
which contains the germs of life. This is followed by a sensation of
peaceful happiness and sleepy relaxation. It is the very greatest
physical pleasure to be had in all human experience, and it helps
very much to increase all other kinds of pleasure also. It is at this
time that married people not only are closest to each other
physically, but they feel closer to each other in every other way
too. It is then most of all that they feel _sure_ they belong to each
other.

The sex act is called by various names, such as coitus, coition,
copulation, cohabitation, sex-intercourse, the sex-embrace, etc. But
all these terms refer to the same thing. The first coitus is apt to
be somewhat painful for the woman, as there is usually a thin
membrane, called the hymen, partly closing the vagina which has to be
broken through, but all women do not have it and it varies in size
and thickness with different people.

Without the sex act, no babies could be created, for it is by this
means only that the semen which contains the male part of the germ of
life can meet the ovum or the female part of the germ of life. When
the two parts come together in the woman's body under just the right
conditions, a baby begins to grow--at first so tiny that it could
hardly be seen without a microscope, and finally, after nine months'
growth in the uterus or womb of the mother till it weighs about seven
or eight pounds, it is born, a live human being. The birth process is
called _labor_, and it is indeed labor, for it usually means much
pain and struggle for the mother, although the baby's journey from
the uterus to the world is only a few inches. It takes anywhere from
an hour to two days for a baby to be born. Doctors are learning more
and more how to lessen the pain, and by the end of another generation
it ought to be possible for child-birth to be practically painless
for most women. By that time people will more generally understand
how to have babies _only_ when they want them and can afford them. At
present, unfortunately, it is against