e variation may be even greater.
Dalton describes the process as follows:--

"When the expected period is about to come on, the female is affected
by a certain degree of discomfort and lassitude, a sense of weight in
the pelvis, and more or less disinclination to society. These symptoms
are in some cases slightly pronounced, in others more troublesome. An
unusual discharge of vaginal mucus then begins to take place, which
soon becomes yellowish or rusty brown in color, from the admixture of
a certain proportion of blood; and by the second or third day, the
discharge has the appearance of nearly pure blood. The unpleasant
sensations which were at first manifest, then usually subside; and the
discharge, after continuing for a certain period, begins to grow more
scanty. Its color changes from a pure red to a brownish or rusty tinge,
until it finally disappears altogether, and the female returns to her
ordinary condition."

The menstrual function continues active from puberty to about the
forty-fifth year, or during the period of fertility. When it finally
disappears, the woman is no longer capable of bearing children. The
time of disappearance is termed the "change of life," or _menopause_.
Exceptional cases occur in which this period is greatly hastened,
arriving as early as the thirty-fifth year, or even earlier. Instances
have also been observed in which menstruation continued as late as the
sixtieth year, and even later; but such cases are very rare; and if
procreation occurs, the progeny is feeble and senile.

With rare exceptions, the function is suspended during pregnancy, and
usually, also, during the period of nursing.

Nature of Menstruation.--There has been a great amount of speculation
concerning the cause and nature of the menstrual process. No entirely
satisfactory conclusions have been reached, however, except that it
is usually accompanied by the maturation and expulsion from the ovary
of an ovum, which is termed ovulation. But menstruation may occur
without ovulation, and, _vice versa_.

Menstruation is not peculiar to the human female, being represented
in the higher animals by what is familiarly termed the "rut." This is
not usually a bloody discharge, however, as in the human female, though
such a discharge has been observed in the monkey.

It has been quite satisfactorily settled that the discharge of the ovum
from the ovary generally takes place about the time of the cessation
of the flow. Imme