326 FRAGMENTS OF SCIENCE 



as the germs of the life observed ? The name of Baron 

 Liebig has been constantly mixed up with these discus- 

 sions. "We have," it is said, "his authority for assum- 

 ing that dead decaying matter can produce fermentation." 

 True, but with Liebig fermentation was by no means sy- 

 nonymous with life. It meant, according to him, the shak- 

 ing asunder by chemical disturbance of unstable molecules. 

 Does the life of our flasks, then, proceed from dead par- 

 ticles? If my co- inquirer should reply "Yes," then I 

 would ask him, "What warrant does Nature offer for such 

 an assumption ? Where, amid the multitude of vital phe- 

 nomena in which her operations have been clearly traced, 

 is the slightest countenance given to the notion that the 

 sowing of dead particles can produce a living crop ?' ' 

 With regard to Baron Liebig, had he studied the revela- 

 tions of the microscope in relation to these questions, a 

 mind so penetrating could never have missed the signifi- 

 cance of the facts revealed. He, however, neglected the 

 microscope, and fell into error but not into error so gross 

 as that in support of which his authority has been in- 

 voked. Were he now alive, he would, I doubt not, repu- 

 diate the use often made of his name Liebig' s view of 

 fermentation was at least a scientific one, founded on pro- 

 found conceptions of molecular instability. But this view 

 by no means involves the notion -that the planting of 

 dead particles "Sticks toff splittern" as Cohn contemptu- 

 ously calls them is followed by the sprouting of infuso- 

 rial life. 



Let us now return to London and fix our attention on 

 the dust of its air. Suppose a room in which the house- 

 maid has just finished her work to be completely closed, 



