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Page:Popular Science Monthly Volume 40.djvu/785

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By Prof. H. W. CONN.

THERE have been no discoveries in the last half-century more startling than those which are now accumulating upon the subject of bacteriology. Every one knows to-day that bacteria have a causal connection with certain diseases, and the whole civilized world has been recently agitated over the attempts that are being made to combat their effect in the human system. The study of the relation of these organisms to the animal body seems to be producing a revolution in the study of medicine, or rather perhaps is creating a science of medicine, for medicine of the past can hardly be called a science.

We have heard so much of the disease-germs and their evil effects that bacteria are usually looked upon as unmitigated nuisances. It is a doubtful chance if any knowledge of their beneficial effects has passed beyond the reach of the scientist's laboratory and lecture-room. But science has for a long time known that even the bacteria which are not connected with disease are of immense significance in the processes of Nature. The non-pathogenic germs were studied long before the pathogenic forms; but the great attraction offered by the study of disease has led the larger number of bacteriologists in this direction. To-day, however, we are beginning to recognize more than ever the great part played by the harmless bacteria, and to find out that their value in the world far outweighs the injury produced by their mischievous relatives. There is hardly a process in Nature which is not in some way connected with bacteria growth. Fermentation, the raising of bread, the formation of vinegar, the germination of seedlings, the growth of plants, the ripening of fertilizers, the decomposition of animal and vegetable bodies by means of which they are again incorporated into the soil, are all to a greater or less extent dependent on the growth of micro-organisms, either bacteria or yeasts. Without the agency of these organisms to prepare the soil, plants could not grow, and life would soon disappear.

There is no one who is not directly or indirectly connected with the dairy industry. The discoveries of the last twenty years, and more especially those of the last five years, have shown that dairy products are in a large measure connected with the growth of microscopic organisms—some dairy processes, indeed, being nothing more than gigantic breeding experiments. Each of the three chief products of the dairy—milk, butter, and cheese—has its own definite relations to bacteria growth and each must be considered separately.

Milk.—The souring of milk is such a universal phenomenon