System_ (1861), to the effect
that season is a more powerful influence on the system than
temperature or atmospheric pressure; "in the early and middle
parts of spring every function of the body is in its highest
degree of efficiency," while autumn is "essentially a period of
change from the minimum toward the maximum of vital conditions."
He found that in April and May most carbonic acid is evolved,
there being then a progressive diminution to September, and then
a progressive increase; the respiratory rate also fell from a
maximum in April to a minimum maintained at exactly the same
level throughout August, September, October, and November;
spring was found to be the season of maximum, autumn of minimum,
muscular power; sensibility to tactile and temperature
impressions was also greater in spring.

Kulischer, studying the sexual customs of various human races,
concluded that in primitive times, only at two special
seasons--at spring and in harvest-time--did pairing take place;
and that, when pairing ceased to be strictly confined to these
periods, its symbolical representation was still so confined,
even among the civilized nations of Europe. He further argued
that the physiological impulse was only felt at these periods.
(Kulischer, "Die geschlechtliche Zuchtwahl bei den Menschen in
der Urzeit," _Zeitschrift fuer Ethnologie_, 1876, pp. 152 and
157.) Cohnstein ("Ueber Praedilectionszeiten bei Schwangerschaft,"
_Archiv fuer Gynaekologie_, 1879) also suggested that women
sometimes only conceive at certain periods of the year.

Wiltshire, who made various interesting observations regarding
the physiology of menstruation, wrote: "Many years ago, I
concluded that every women had a law peculiar to herself, which
governed the times of her bringing forth (and conceiving); that
she was more prone to bring forth at certain epochs than at
others; and subsequent researches have established the accuracy
of the forecast." He further stated his belief in a "primordial
seasonal aptitude for procreation, the impress of which still
remains, and, to some extent, governs the breeding-times of
humanity." (A. Wiltshire, "Lectures on the Comparative Physiology
of Menstruation," _British Medical Journal_, March, 1883, pp.
502, etc.)

Westermarck, in a chapter of his _History of Human Mar