Page:Popular Science Monthly Volume 7.djvu/180

168 be found to be the same both in physiological and pathological development.

Most prominent among the conditions necessary to secure the normal progress of physiological development is warmth; and nothing more decidelydecidedly [sic] interferes with it, or more quickly arrests it, than exposure to cold. In fact, an elevated temperature is the initial power—the first mover of the developmental process in all organisms, vegetable as well as animal. It is solar heat that forces the seed to germinate, the plant to bud, and the flower to bloom. Without warmth the fecundated egg of the oviparous animal would ever remain an inert mass; hence the snake deposits her germs in a dunghill of rotting vegetable matter where they may be warmed by the heat of fermentation. The ostrich intrusts her egg almost entirely to the sun-baked sand of the African desert; and birds in general incubate for days or weeks to supply the necessary heat for securing the development of their eggs. Fish inhabiting waters that are deep and cold, seek shallower and warmer streams in which to deposit their spawn. The difference between the warm and the cold seasons of the year, as regards the prevalence of reproduction, in both animals and plants, is familiar to every one.

But, besides heat being the primum mobile of normal evolution, it is equally necessary to maintain it when already begun. Exposure to cold is fatal. The shivering of young animals—their great liability to become chilled on exposure-to a depressed temperature—has been observed by every one; and in the breeding of domestic animals, as in the cultivation of plants, there is probably no more potent source of mortality than insufficient warmth; and, further, this mortality is found to be more prevalent during unusually cold seasons. Now, the young of our own species form no exception to this rule; they, too, are liable to suffer a fatal arrest of physiological development on being exposed to cold. Thus, in a statistical inquiry as to the average number of deaths at different seasons, and at different ages, from a table prepared by M. Quetelet, of Brussels, it appears that, during the first month of infant life, the external temperature has a very marked influence; for the average mortality during each of the three summer months being 80, that of January is nearly 140, and the average of February and March 125. This is confirmed by the result obtained by MM. Villermé and Milne-Edwards in their researches on the mortality of the children conveyed to the foundling hospitals in the different towns in France; for they not only ascertained that the mortality is much the greatest during the first three months in the year, but also that it varies in different parts of the kingdom according to the relative severity of the winter.

Additional proof of the disastrous influence of cold in early life, and, by-the-way, an explanation of the apparent natural defect in