324 FKAGMENTS OF SCIENCE. 



chambers, exposed to optically pure air. The one is a 

 mineral solution containing in proper proportions all 

 the substances which enter into the composition of 

 bacteria, the other is an infusion of turnip it might be 

 any one of a hundred other infusions, animal or vegeta- 

 ble. Both liquids are as clear as distilled water, and 

 there is no trace of life in either of them. They are, 

 in fact, completely sterilised. A mutton-chop, over 

 which a little water has been poured to keep its juices 

 from drying up, has lain for three days upon a plate in 

 our warm room. It smells offensively. Placing a drop 

 of the fetid mutton-juice under a microscope, it is found 

 swarming with the bacteria of putrefaction. With a 

 speck of the swarming liquid I inoculate the clear 

 mineral solution and the clear turnip infusion, as a 

 surgeon might inoculate an infant with vaccine lymph. 

 In four-and-twenty hours the transparent liquids have 

 become turbid throughout, and instead of being barren 

 as at first they are teeming with life. The experiment 

 may be repeated a thousand times with the same in- 

 variable result. To the naked eye the liquids at the 

 beginning were alike, being both equally transparent 

 to the naked eye they are alike at the end, being both 

 equally muddy. Instead of putrid mutton-juice, we 

 might take as a source of infection any one of a hun- 

 dred other putrid liquids, animal or vegetable. So 

 long as the liquid contains living bacteria a speck of it 

 communicated either to the clear mineral solution, or to 

 the clear turnip infusion, produces in twee ty-f our hours 

 the effect here described. 



We now vary the experiment thus : Opening the 

 back-door of another closed chamber which has con- 

 tained for months the pure mineral solution and the 

 pure turnip infusion side by side, I drop into each of 

 them a small pinch of laboratory dust. The effect here 



