So persistent a disturbing element in spring and autumn suggests that some physiological conditions underlie it, and that there is a real metabolic disturbance at these times of the year. So few continuous observations have yet been made on the metabolic processes of the body that it is not easy to verify such a surmise with absolute precision. Edward Smith's investigations, so far as they go, support it, and Perry-Coste's long-continued observations of pulse-frequency seem to show with fair regularity a maximum in early spring and another maximum in late autumn.[[174]] I may also note that Haig, who has devoted many years of observations to the phenomena of uric-acid excretion, finds that uric acid tends to be highest in the spring months, (March, April, May) and lowest at the first onset of cold in October.[[175]]
Thus, while the sexual climaxes of spring and autumn are rooted in animal procreative cycles which in man have found expression in primitive festivals—these, again, perhaps, strengthening and developing the sexual rhythm—they yet have a wider significance. They constitute one among many manifestations of spring and autumn physiological disturbance corresponding with fair precision to the vernal and autumnal equinoxes. They resemble those periods of atmospheric tension, of storm and wind, which accompany the spring and autumn phases in the earth's rhythm, and they may fairly be regarded as ultimately a physiological reaction to those cosmic influences.
F. Smith, Veterinary Physiology; Dalziel, The Collie.
Mondière, Art "Cambodgiens," Dictionnaire des Sciences Anthropologiques.