SPONTANEOUS GENERATION. 577 



ing to him, the shaking asunder by chemical disturbance 

 of unstable molecules. Does the life of our flasks, then, 

 proceed from dead particles? If my co-inquirer should 

 reply "Yes," then I would ask him, " What warrant does 

 nature offer for such an assumption? Where, arnid the 

 multitude of vital phenomena 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 revelations of the microscope in relation to these ques- 

 tions, a mind so penetrating could never have missed the 

 significance 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, repudi- 

 ate the use often made of his name Liebig's view of fer- 

 mentation was at least a scientific one, founded on profound 

 conceptions of molecular instability. But this view by no 

 means involves the notion that the planting of dead particles 

 " Stickstoffsplittern "as Cohn contemptuously calls them 

 is followed by the sprouting of infusorial 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, 

 with the exception of an aperture in a shutter through 

 which a sunbeam enters and crosses the room. The float- 

 ing dust reveals the track of the light. Let a lens be placed 

 in the aperture to condense the beam. Its parallel rays are 

 now converged to a cone, at the apex of which the dust is 

 raised to almost unbroken whiteness by the intensity of its 

 illumination. Defended from all glare, the eye is peculiarly 

 sensitive to this scattered light. The floating dust of Lon- 

 don rooms is organic, and may be burned without leaving 

 visible residue. The action of a spirit-lamp flame upon the 

 floating matter has been elsewhere thus described: 



In a cylindrical beam which strongly illuminated the dust of our 

 laboratory, I placed an ignited spirit-lamp. Mingling with the flame, 

 and round its rim, were seen curious wreaths of darkness resembling 

 an intensely black smoke. On placing the flame at some distance 

 below the beam, the same dark masses stormed upward. They 

 were blacker than the blackest smoke ever seen issuing from the 

 funnel of a steamer; and their resemblance to smoke was so perfect 



