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Show 80 ORIGINATION OF LIVING BEINGS. been floating about in the mr and had got caged In this way. I-Ie went farther, and said to himself, "If these really are the things that give rise to the appearance of spontaneous generation, I ought to be able to take a ball of this dusted gun-cotton and put it into one of my vessels, containing that boiled in:usion. which ~as been kept away from the air, and In whiCh no Infusoria are at present developed, and then, if I am right, the introduction of this gun-cotton will give rise . )) to organisms. . Accordingly, he took one of these vessels of In-fusion which had been kept eighteen months, without ' . . the least appearance of life, and by a most Ingen1~us contrivance, he managed to break it open and Introduce such a ball of gun-cotton, without allowing the infusion or the cotton ball to come into contact with any air but that which had been subjected to. a red heat, and in twenty-four hours he had the satisfaction of finding all the indications of what had been hitherto called spontaneous generation. He had succeeded in catching the germs and developing organisms in the way he had anticipated. It now struck him that the truth of his conclusions miO'ht be demonstrated without all the apparatus he had employed. To do this, he took some decaying animal or vegetable substance, such as urine, which is an extremely decomposable substance, or the juice of yeast, ~r perhaps some other artificial preparati~n, and filled a vessel having a long tubular neck, with it. l-Ie then boiled the liquid and bent that long neck ORlGINATI ON OF LIVING BEINGS. 81 into an S shape or zig-zag, leaving it open at the end. The infusion then gave no trace of any appearance of spontaneous generation, however long it might be left, as all the germs in the air were deposited in the beginning of the bent neck. He then cut the tube close to the vessel, and allowed the ordinary air to have free and direct access ; and the result of that was the appearance of organisms in it, as soon as the infusion had been allowed to stand long enough to allow of the growth of those it received from the air, which was about forty-ejght hours. The result of M. Pasteur's experiments proved, therefore, in the most conclusive manner, that all the appearances of spontaneous generation arose from nothing more than the deposition of the germs of organisms which were constantly floating in the air. To this conclusion, l1owever, the objection was made, that if that were the canse, then the air would contain such an enormous number of these germs, that it would be a continual fog. But M. Pasteur replied that they are not there in anything like the number we might suppose, and that an exaggerated view has been held on that subject; he showed that the chances of animal or vegetable life appearing in infusions, depend entirely on the conditious under which they are exposed. If they are exposed to the ordinary atmosphere around us, why, of course, you may have organisms appearing early. But, on the o her haud, if they are exposed to air from a great height, or from some very quiet cellar, you will often not find a single trace of life. |