Page:Popular Science Monthly Volume 37.djvu/826

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N the natural competitive strife for existence among all organic beings, man had formerly recognized the fact that he was in direct antagonism with opponents which were formidable in proportion to their size, strength, and ferocity; and against whose aggressions he was to measure force, guided by his best intelligence. It has been, of course, a matter of common observation from most primitive times that some mysterious, invisible influence was constantly at war upon human life, but whose nature and intent were believed to be beyond permissible human ken. Scarcely a ray of light seems to have been shed upon this occult cause of human destruction until the present century; indeed, until within the last score of years. It is true, microscopy had been gradually unveiling to our astonished vision a new world, teeming with life of incalculable activity and scientific importance. But only recently have improved instruments and methods transformed a former invisible field into a true vivarium of beings, each having its distinctive size, color, form, requirement for food and place, with its cycle of birth, life, and death peculiar to its species.

It is now understood that our material world, with its visible occupants, is supplemented by and interdependent with myriads of micro-organisms, permeating or enveloping all matter, and whose relation to organic life is essentially cosmical. In some of their multifarious forms they are the direct and only means and medium of transformation of material from its cruder form into the appropriate food for all organic beings; apparently having the power of wresting atom from atom in the mineral world in order to render it available for themselves as well as for plants and animals; thus performing a work purely beneficent and essential. Other forms of minute organisms are employed in the mutations of nature in undoing the work of the former; and, as if endowed with a spirit of maleficence, are occupied solely with the work of decomposing all organic substances, inducing decay and death.

These bodies are of the so-called low forms of life; impelled by natural necessities to provide for themselves where and as best they may. They are of independent vitality, each individual having its definite organization and requirement as to kind of food, temperature, and amount of light and air. They belong to distinct species, and are reproduced in kind, with as much exactitude in size and form as are the large plants and animals, both of which natural divisions they represent.