Page:Popular Science Monthly Volume 15.djvu/791

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moving from place to place, although many enjoy this freedom for only a part of their lifetime, and then become adherent or attached to foreign bodies for the rest of their existence. But even with the most rapid, free swimming forms, so little distance can be accomplished in their almost momentary lives, that their voluntary progressions can have little or no effect on their geographical distribution. In this they are creatures of chance or circumstance. Multiplying in myriads, and being too small and weak to resist the elements, they are constantly swept about in currents of water or air, and in the moisture on the surfaces of moving animals, etc. Well-authenticated observations show that with the evaporation of ponds and other waters containing swarms of these little animals, many encyst themselves within delicate capsules formed of an exudation, which hardens the body-surface; they then dry up and become as particles of dust, which are wafted from place to place by the winds, and for weeks or months may lie in the mud, dust, or snow, on hay, moss, branches of trees, etc. Others decompose, but leave behind their germs, which are distributed in the same way. By these means they are scattered everywhere, and those which chance to fall into favorable situations survive and produce swarms of progeny, while others, falling on bad ground, perish. Thus they are ready to do their appointed work, whenever and wherever it is needed. It is commonly thought that pure drinking-water is filled with these microscopic creatures, and it is sometimes said that they constitute the life of the water, while in their absence it becomes dead, stagnant, and often slimy, green, and unfit for use. All this is the opposite of the facts. Pure water is not inhabited by organisms; on the contrary, stagnant water or impure water alone affords them subsistence. They hasten the destruction of dead animal and vegetable matters the water may contain, causing for the time being an infusion or fermentation, which results finally in the purification of the liquid in question.

The bodily corruption in diseases, whether contagious or not, is not caused alone by the swarms of infesting organisms associated therewith, but is simply their cause, a sustenance for them, itself making their existence and multiplication possible.

The unaccounted-for readiness of these animalcules to spring up wherever decaying organic matter existed, first suggested the name infusoria, and led to the early false opinions that they were generated by the decomposition and fermentation of organic bodies, and to the modern reformed theory of spontaneous generation.

Strangely seeming, yet true, stagnation, death, decay, are replete with life when viewed through lenses, so that it has become a scientific doctrine that all organic decomposition and fermentation is assisted and sustained by these tiny creatures. Hence we may regard them as the most important scavengers of earth, water, and air.

While their devouring work is as a "bottling up" of injurious and