Page:Popular Science Monthly Volume 56.djvu/393

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times the lake dried up, and again it has overflowed and inundated the low lands in the neighborhood, as in 1827 and 1862. Often its water has been set boiling by escaping gases. It would be interesting to know what varying pressure caused the changes in the level of this lake on the top of Mount Catarman.

A further idea of the volcanic activity of this region may be gained from the circumstance that a volcanic island emerged from the sea on the north coast of Luzon in 1856, which grew to seven hundred feet in height by 1860, and is now about eight hundred feet high. Every one has seen photographs of the streets of Manila after an earthquake, which form of subterranean activity is so common that it is taken into account in building.



THE labors of M. Metchnikoff have made known one of the most curious mechanisms—perhaps the most effective—which Nature employs to protect the organism against the invasion and ravages of microbes. We are only beginning to learn the means which are provided for our defense against the countless swarms of enemies of this class, some of them exceedingly dangerous, among which we have to live and move. In the first rank of these defenses is phagocytosis. The struggle of the organism against its minute assailants is an image of human wars. The cutaneous or mucous integument, continuous over the whole body, constitutes a kind of fortified inclosure which the microbe can not penetrate, except where some breach has been made. On one side of that wall, in the living city, the phagocytes or leucocytes (white cells) form an immense defensive army in a state of continual mobilization, or, as M. Duclaux would say, an innumerable and vigilant police.

These phagocytes or leucocytes are the nomadic elements of our economy. The animal body may be compared to an organized city in which all the living corpuscles, all the cellular elements, are sedentary, each having its place and staying there. Hence the comparison, often made, with the stones of a building, which is not exact, however, because these vital elements grow and increase, enlarging the structure without change of arrangement, while the stones do not. The growth and nutrition of these anatomical elements, it should be added, are carried on exclusively at the expense of liquid matters. Nothing solid can enter them or come out from them.