Page:Popular Science Monthly Volume 5.djvu/566

548 factions are connected, exist in the air. This is one of the conclusions, and perhaps the most legitimate and most fertile one, of M. Pasteur's striking studies.

He deserves the glory of it precisely because he has not priority in it. In truth, the originator of this idea only had, and could only have, a dim intuition of it. He could measure neither its importance nor its consequences. The importance and the results of a great idea, whatever it may be, only become apparent when, after undergoing a certain evolution, it has gained the precision, certitude, and establishment, that nothing but long experience can confer upon it. A conception must have acquired some age in science to wear a fixed authority, and bestow fame on those who comprehend, and cause to be comprehended, all its grandeur and power. The circulation of the blood had long been seen by glimpses, in the schools of physiology, when Harvey gave it complete and vigorous demonstration. Gravitation had long invited research, and suggested presentiment, before Newton drew its perfect system. So, too, the panspermist theory, neglected and ignored since the time of its earliest authors—among whom Astier, in 1813, deserves particular mention—has only been definitely established in our time, through the experiments made by M. Pasteur. These experiments, repeated and varied in a thousand ways, all refer to the investigation, by comparison of what takes place in the same fermentable liquid, under the different conditions of exposure to common air, filled with dust, and of contact with purified air. For instance, M. Pasteur puts a certain quantity of a liquid, that readily undergoes change, into glass balls through which a current of air may be made to pass. Fermentation and the development of small organisms take place very soon in the balls through which common air circulates; but, if the air, before entering them, passes through a plug of cotton, no change in the liquid is observed. When the volume of air, thus filtered through cotton, is considerable, the plug is so filled with dust as to turn black. Now, this dust, in addition to a quantity of mineral particles, and fluff of many kinds, contains spores and germs of fermenting substance, as is proved by the fact that the smallest quantity of it, sprinkled in pure liquid, will produce fermentation in it. An experiment of another kind is this: M. Pasteur, by an ingenious arrangement, inserts and withdraws from a glass jar, filled with pure air, the juice from the inside of a single grape, so that, during the experiment, the juice communicates neither with the surface of the grape nor with the atmospheric air. The juice, thus obtained, shows no trace of fermentation, remaining unchanged as long as the jar is closed; but, if it is opened, or if its contents are mixed with a few drops of water in which the surface of the grape has been washed, fermentation is set up in it at once. This is because the outside of grapes is always covered with yeast-germs, even when the bunches have been subjected to constant rains. In this case, plainly, fermentation is due