312 THE FLOATING-MATTER OF THE AIR. 



employed. In three days, however, after its infection 

 with the dust, the turnip-infusion is muddy, and swarm- 

 ing as before with bacteria. But what about the mineral 

 solution which, in our first experiment, behaved in a 

 manner undistinguishable from the turnip-juice? At 

 the end of three days there is not a bacterium to be 

 found in it. At the end of three weeks it is equally 

 innocent of bacterial life. We may repeat the experi- 

 ment with the solution and the infusion a hundred 

 times with the same invariable result. Always in the 

 case of the latter the sowing of the atmospheric dust 

 yields a crop of bacteria — never in the former does the 

 dry germinal matter kindle into active life.^ What 

 is the inference which the reflecting mind must draw 

 from this experiment ? Is it not as clear as day that 

 while both liquids are able to feed the bacteria and to 

 enable them to increase and multiply, after they have 

 been once fully developed, only one of the liquids is 

 able to develope into active bacteria the germinal dust 

 •of the air ? 



I invite my friend to reflect upon this conclusion ; 

 he will, I think, see that there is no escape from it. 

 He may, if he prefers, hold the opinion, which I 

 •consider erroneous, that bacteria exist in the air, not 

 as germs but as desiccated organisms. The inference 

 remains, that while the one liquid is able to force the 

 passage from the inactive to the active state, the other 

 is not. 



But this is not at all the inference which has been 

 drawn from experiments with the mineral solution. 

 Seeing its ability to nourish bacteria when once inocu- 

 lated with the living active organism, and observing 



* This is the deportment of the mineral solution as described by- 

 others. My own experiments would lead me to say that the de- 

 velopment of the bacteria, though exceedingly slow and difficult, is 

 not impossible. 



