Page:Popular Science Monthly Volume 17.djvu/849

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clothing, pieces of different clothing materials were impregnated with strong putrefying and bacteria-bearing fluids, then dried slowly, and kept for a long time without protection against external influences. Whenever the smallest piece of one of these materials was put into a suitable fluid, the perturbation invariably took place which is the sure sign of the active multiplication of bacteria. Clothing which had not been impregnated did not excite this perturbation, or only in an insignificant degree. Specimens of the defiled clothing which were placed in a similar solution after they had been exposed for five minutes to a temperature of from 125° to 150° C, or for one or two minutes to a higher temperature, produced no change. The capacity of the bacteria to resist heat varies widely among the different species, and appears to depend largely on the faculty of developing spores. The individuals are killed, but the spores remain vital. The increase of any one kind is limited by the presence of other kinds, with which a struggle for existence has to be maintained.

No increase of bacteria takes place without the presence of a suitable substance to support them. The most favorable of non-nitrogeneous substances is sugar; among nitrogeneous substances the most favorable are the albuminoids; among mineral matters, potash, phosphorus, magnesia, and sulphur. If the supporting substance, even though it is needed in only a minute quantity, is consumed, or if it is present in great excess, a pause in the development, but not the death of the bacteria, takes place. A similar effect is produced by taking away the water, but, when the water is restored, an increase of life again takes place.

The practical object of disinfection should be to go beyond securing a suspension of animation of the bacteria, and to seek to destroy the vitality of the spores. Neither years of dryness, nor months of exposure in foul water, nor repeated drying and moistening, will injure the fertility of these germs.

An excess of water produces a similar effect with desiccation upon the vital conditions of the bacteria. A great dilution of the supporting fluid by the infusion of pure water will in a short time produce a suspension of the process of decomposition. Privation of light has no effect. The operation of electricity has not been enough observed to justify the drawing of any conclusion. The effect of the privation of air has not been fully determined. It was once thought that the development of bacteria could be hindered by the removal of oxygen, but this is doubtful. Oxygen greatly speeds the development, but it can take place without it. Bacteria are not developed in nitrogen, hydrogen, carbonic oxide, carbonic acid, nitrous oxide, and illuminating gas.

The substances which are fatal to the life of the bacteria next demand attention. Among these, the concentrated mineral acids, iodine, bromine, chlorine, the sulphates of copper and zinc, corrosive subli-