But this faculty of adaptation to the different seasons inherent in the body is only observed in the better constitutions. That it may be manifested, it is necessary there be present a certain energy of the nervous system ; without this even the moderate colds of winter will not be resisted. Without this the adult will have a constitution that will present analogies with that of early infancy. At present we merely mention the kind of constitution ; we shall return to the subject by-and-by.
Differences according to the nature of the climate.—The preceding facts render direct ex periments to ascertain the influence of the tem perature of different climates on the calorific power altogether unnecessary. This is so far fortunate ; for it were no easy matter to institute them to the extent and with the precautions necessary to security and satisfaction. The knowledge of these effects is a necessary con sequence of the researches that precede. The temperature of warm climates is represented by the summer temperature of temperate climates, with this difference, that it is higher, and that with slight variations it continues through the whole year. Whence it follows that warm climates taken generally must produce effects upon the constitution analogous to those pro duced by summer with us, only of greater intensity by reason of the higher thermometric range and longer continuance of the heat. The
inhabitants of hot climates ought consequently to have an inferior degree of calorific power than those of temperate or cold countries, what ever be the season. And we find, in fact, that the natives of the warmer latitudes of the earth present the characters in general that distinguish the constitution of the body in the summers of temperate countries, and characterizes the second period of youth—more rapid motions of the circulatory and respiratory systems, and a higher temperature, conjoined with an inferior degree of energy in the functions of innervation and nutrition.
We shall not here enter upon the examina tion of the effects upon the natives of these warmer latitudes from change of climate. We shall speak of this elsewhere. After the periodi cal changes depending on the seasons we shall pass to others of shorter duration, but which revert much more frequently, and are under the influence of other causes.