264 NATURE AND LIFE. 



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 

 Pasteur. That famous chemist has improved a vague 

 sketch into a finished and masterly drawing. These experi- 

 ments, 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 con- 

 tact with purified air. For instance, Pasteur puts a cer- 

 tain 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 : 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, fermenta- 

 tion is set up in it at once. This is because the outside of 

 grapes is always covered with yeast-germs, even when the 



