Page:Popular Science Monthly Volume 6.djvu/415

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IVING organisms, microscopical in size, of the simplest, most elementary nature, and moving freely in different liquids, have been known to observers for nearly two hundred years. Scientific classification and description were long impossible, on account of the meagre facilities furnished by the microscopes of the last century; but, during the last fifty years, the means of observation have been so much improved, and the number of observers has been so great, that the advance in our knowledge of microscopical bodies compares favorably with that in other branches of science. This advance has been greatly stimulated by a tendency to see in low vegetable or animal organisms the exciting cause not only of fermentation and decomposition, but also of many diseases. Pasteur's researches into the nature and causes of fermentation, the lectures and publications of Tyndall and Huxley, and the bitter discussions about spontaneous generation, have made us all familiar with the names bacteria, vibriones, and micrococci, or microzymas, with which we associate the idea of microscopical

 Fig. 1.—a, Micrococci; d, Micrococci, multiplying by scission: b, c. Bacteria (rod Bacteria, B. termo; e, vibriones; f, h, i, k, Torulæ, or Yeast-Plant, sprouting; g, probably "Dauersporen," durable or resting spores.

bodies, round, oval, or rod-like and jointed, varying in length from five ten-thousandths to one one-hundredth of a millimetre, and found especially in putrefying vegetable and animal infusions. The term micrococcus has always been restricted to the small, round, or ovoid bodies, but bacterium and vibrio have been applied indiscriminately to all, the former being more commonly used in France and Germany, the latter in England. When used in the narrower sense, bacteria denotes stiff, rod-like bodies, single or jointed, motionless or endowed with an oscillatory movement in place, while vibrio is applied to those which move rapidly across the field of the microscope with an