Page:Popular Science Monthly Volume 7.djvu/739
CROLL ON CLIMATE AND TIME.
other to which, in turn, it serves as food. And observation shows that, so long as there remains any organic matter which can furnish carbon, the life of the moulds or of the infusoria is prolonged, but always with the result of setting free, in the form of carbonic acid-gas, a part of the carbon, while the life draws its other materials from the mineral salts and from the nitrogen of the ammonia compounds. The saline substances indeed are very abundant, for at no time have they been able to take on the gaseous form. And, finally, what remains? 1. Ashes, as if fire had been applied to the matter, for these slow successive combustions have produced the effect of fire; 2. The last germs of the last beings which lived upon the remains of their fellows. The mineral substances are ready to return to the soil, the organic matter has passed into the air, and when all shall have become dry the spores of the moulds and the cysts of the infusoria will be borne away upon the wings of the wind, to recommence, elsewhere, their work of life and of destruction of life.
The ferments, and especially the aërobic ferments or the beings which are like them, are then the ferments of the ferments.
After the anaërobic ferments have commenced the disorganization of the material, the aërobic beings intervene and burn the organic matter as completely as it would be burned by fire—more slowly, it is true, but of what importance is time in the work of destruction by the life of germs?—for it is in them alone that resides the perpetuity of the life of microscopic beings.
THE distribution of temperatures upon the globe is a subject of profound popular and scientific interest. More than any other, it affects the distribution of living forms, not only in zones of climate, but in geological time. The contour of the earth's surface, and the relations of land and water upon it, may produce important local changes, or establish local faunas and floras, but these are scarcely more than modifications of grander and more general results. Arctic plants may, indeed, flourish under the equator, but only on mountains where an arctic climate prevails. Heat determines the limits equally of the vine, the palm of the tropics, the cereals of the temperate zone, and. the food of the reindeer. Whether or not tree-ferns grow in Pennsylvania, and forests of pine in the Arctic Circle, depends on cli-
- Climate and Time in their Geological Relations: a Theory of Secular Changes of the Earth's Climate. By James Croll, of Her Majesty's Geological Survey of Scotland. New York: D. Appleton & Co. 1875