y annual period of flowering in plants, with its
play of sperm-cell and germ-cell and consequent seed-production, through
the varying sexual energies of animals, up to the monthly effervescence of
the generative organism in woman, seeking not without the shedding of
blood for the gratification of its reproductive function, from first to
last we find unfailing evidence of the periodicity of sex. At first the
sun, and then, as some have thought, the moon, have marked throughout a
rhythmic impress on the phenomena of sex. To understand these phenomena we
have not only to recognize the bare existence of that periodic fact, but
to realize its implications.

Rhythm, it is scarcely necessary to remark, is far from characterizing
sexual activity alone. It is the character of all biological activity,
alike on the physical and the psychic sides. All the organs of the body
appear to be in a perpetual process of rhythmic contraction and expansion.
The heart is rhythmic, so is the respiration. The spleen is rhythmic, so
also the bladder. The uterus constantly undergoes regular rhythmic
contractions at brief intervals. The vascular system, down to the smallest
capillaries, is acted on by three series of vibrations, and every
separate fragment of muscular tissue possesses rhythmic contractility.
Growth itself is rhythmic, and, as Malling-Hansen and subsequent observers
have found, follows a regular annual course as well as a larger cycle. On
the psychic sides attention is rhythmic. We are always irresistibly
compelled to impart a rhythm to every succession of sounds, however
uniform and monotonous. A familiar example of this is the rhythm we can
seldom refrain from hearing in the puffing of an engine. A series of
experiments, by Bolton, on thirty subjects showed that the clicks of an
electric telephone connected in an induction-apparatus nearly always fell
into rhythmic groups, usually of two or four, rarely of three or five, the
rhythmic perception being accompanied by a strong impulse to make
corresponding muscular movements.[75]

It is, however, with the influence--to some extent real, to some extent,
perhaps, only apparent--of cosmic rhythm that we are here concerned. The
general tendency, physical and psychic, of nervous action to fall into
rhythm is merely interesting from the present point of view as showing a
biological predisposition to accept any periodicity that is habitually
imposed upon the organism.[76] Menstruation has