Page:Popular Science Monthly Volume 20.djvu/849

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ent in the solution, and if the solutions were then carefully sealed up free from air. Nor was it necessary to exclude the air, provided that pure air, free from germs, were admitted. By passing the air through red-hot tubes or through gun-cotton before reaching the solutions, he found that the development of organisms, in such boiled solutions, did not take place. [A single exception was noticed in the case of milk, which required a higher temperature to destroy the organisms.]

Professor Pasteur also examined the gun-cotton through which the air had been passed, and he found, among other things, certain cells to which he attributed the power of causing the growth of organisms in solutions. By sowing some of these cells in solutions which had previously remained clear, and finding that such solutions speedily became turbid from the growth of living organisms, it was proved that the air which had passed through the gun-cotton had lost its property of causing the development of life in solutions, because the germs which the air contained had been stopped by the gun-cotton." The results on this point might be summed up: "1. No organisms are developed in solutions if care be taken to prevent the possibility of the presence of germs; 2. This negative result does not depend upon the exclusion of oxygen; 3. The matter separated from ordinary air is competent to develop organisms in solutions which previously had remained unchanged. Not less important were the results of Pasteur's experiments respecting the chemical functions of the ferment. . . . He proved that those conditions which are most favorable to the healthy growth and development of the yeast-cell are most conducive to the progress of fermentation, and that fermentation is impeded or arrested by those influences which check the growth or destroy the vitality of the cell. . . . To the biologist, two of Pasteur's researches are of very great importance. He has shown that fungi find all the materials needed for their nutrition and growth in water containing an ammonia salt and certain mineral constituents, and devoid of any nitrogenized organic matter; and he has proved that all the phenomena presented by the destructive silk-worm epidemic, the pébrine (even the singular fact that it is hereditarily transmitted through the female and not through the male), are to be explained by the presence of a parasitic organism in the diseased caterpillars."

M. Pasteur's later researches have been continued in the same direction as those which we have already mentioned, and have resulted in a great expansion of the germ theory and its application to useful purposes. Those which have so far been most fruitful in practical consequences are the investigations which he has made into the cause of the cholera in fowls and of carbuncular diseases in cattle and sheep, and into the means of preventing them by the cultivation of the infectious germs in diluting fluids and inoculation with them—investigations the results of which have already been heralded over the whole earth, and the inestimable value and importance of which have