Page:Popular Science Monthly Volume 41.djvu/844

824 were narrowing at that time toward the north, and that their extremities were pointing toward some spot in the vicinity of what is now the Bering Strait, in the same way as South America, South Africa, and South Australia are now pointing toward the south pole. The great plateau of northeast Asia, which has remained a continent ever since the Devonian age, has so much the shape of South America pointing northeast that the resemblance is simply striking. On the other side, we know that the Miocene flora discovered in Greenland, Spitzbergen, and New Siberia indicates the existence of a great Miocene continent where we now have but the ice-clad arctic archipelagos. So that we must conclude that, while the central (temperate and equatorial) parts of the globe really offer a certain permanence in the disposition and general outlines of their continents, the arctic region stands in a different position. It was under the ocean during a large part of the Secondary period, it emerged from the ocean and was occupied by a large continental mass during the Tertiary period; and now it is again under water. Such being the conditions of the arctic region, we may suppose that the same oscillations took place in the antarctic region as well. In such case, the two circumpolar regions would have been periodically invaded by the ocean (either alternately or during geological epochs closely following each other), and they would have periodically emerged from the sea in the shape of continents more or less indented by gulfs and channels. In short, a certain stability in the distribution of land and water in the equatorial and temperate zones, and unstability in the circumpolar regions (with, most probably, an unstable Mediterranean belt), would perhaps better express the observed facts than a simple affirmation of stability of continents. If these considerations prove to be correct and I venture to express them only as a suggestion for ulterior discussion then the hypothesis of a former more or less close land-connection between the southern extremities of our present continents would not appear unlikely, and the striking similarity between the faunas of Patagonia and Australia would be easily accounted for.

Few branches of science have developed with the same rapidity as bacteriology during the last few years. The idea that infectious diseases are due to some micro-organisms invading the body of the infected animal is certainly old. It was ventilated many