826 FRAGMENTS OF SCIENCE 



as the germs of tlie 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 tofisplittern" 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, 



