548 THE POPULAR SCIENCE MONTHLY, 



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 establish- 

 ment, that nothing but long experience can confer upon it. A concep- 

 tion must have acquired some age in science to wear a fixed authority, 

 and bestow fame on those who comprehend, and cause to be compre- 

 hended, all its grandeur and power. The circulation of the blood had 

 long been seen by glimpses, in the schools of physiology, when Har- 

 vey 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 As- 

 tier, 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 difierent conditions of exposure to com- 

 mon air, filled with dust, and of contact with purified air. For in- 

 stance, 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 organ- 

 isms take place very soon in the balls through which common air cir- 

 culates ; 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. Xow, this dust, in addition to a quantity 

 of mineral particles, and flufl^" 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 ex- 

 periment, 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, fer- 

 mentation 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 



