Edward Smith, also a notable pioneer in this field of human periodicity, and, indeed, the first to make definite observations on a number of points bearing on it, sums up, in his remarkable book, _Health and Disease as Influenced by Daily, Seasonal, and Other Cyclical Changes in the Human 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 für Ethnologie_, 1876, pp. 152 and 157.) Cohnstein ("Ueber Prädilectionszeiten bei Schwangerschaft," _Archiv für Gynäkologie_, 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.)