276 FRAGMENTS OF SCIENCE 



They must be young cells which have caught their vegeta- 

 tive vigor from contact with free oxygen. But once pos- 

 sessed of this vigor the yeast may be transplanted into a 

 saccharine infusion absolutely purged of air, where it will 

 continue to live at the expense of the oxygen, carbon, and 

 other constituents of the infusion. Under these new con- 

 ditions its life, as a plant, will be by no means so vigorous 

 as when it had a supply of free oxygen, but its action as 

 a ferment will be indefinitely greater. 



Does the yeast-plant stand alone in its power of pro- 

 voking alcoholic fermentation ? It would be singular if 

 amid the multitude of low vegetable forms no other could 

 be found capable of acting in a similar way. And here 

 again we have occasion to marvel at that sagacity of ob- 

 servation among the ancients to which we owe so vast a 

 debt. Not only did they discover the alcoholic ferment 

 of yeast, but they had to exercise a wise selection in pick- 

 ing it out from others, and giving it special prominence. 

 Place an old boot in a moist place, or expose common 

 paste or a pot of jam to the air; it soon becomes coated 

 with a blue- green mould, which is nothing else than the 

 fructification of a little plant called Penicillium glaucum. 

 Do not imagine that the mould has sprung spontaneously 

 from boot, or paste, or jam; its germs, which are abun- 

 dant in the air, have been sown, and have germinated, in 

 as legal and legitimate a way as thistle-seeds wafted by 

 the wind to a proper soil. Let the minute spores of 

 Penicillium be sown in a fermentable liquid, which has 

 been previously so boiled as to kill all other spores or 

 seeds which it may contain; let pure air have free access 

 to the mixture; the Penicillium will grow rapidly, striking 

 long filaments into the liquid, and fructifying at its sur- 



