310 FRAGMENTS OF SCIENCE 



taneons generation is not the less valid on this account. 

 Nor is it in any way upset by the fact that others in re- 

 peating his experiments obtained life where he obtained 

 none. Eather is the refutation strengthened by such dif- 

 ferences. Given two experimenters equally skilful and 

 equally careful, operating in different places on the same 

 infusion, in the same way, and assuming the one to obtain 

 life while the other fails to obtain it; then its well-estab- 

 lished absence in the one case proves that some ingredient 

 foreign to the infusion must be its cause in the other. 



Spallanzani' s sealed flasks contained but small quanti- 

 ties of air, and as oxygen was afterward shown to be gen- 

 erally essential to life, it was thought that the absence of 

 life observed by Spallanzani might have been due to the 

 lack of this vitalizing gas. To dissipate this doubt, 

 Schulze in 1836 half filled a flask with distilled water to 

 which animal and vegetable matters were added. First 

 boiling his infusion to destroy whatever life it might con- 

 tain, Schulze sucked daily into his flask air which had 

 passed through a series of bulbs containing concentrated 

 sulphuric acid, where all germs of life suspended in the 

 air were supposed to be destroyed. From May to August 

 this process was continued without any development of 

 infusorial life. 



Here again the [Access of Schulze was due to his work- 

 ing in comparatively pure air, but even in such air his 

 experiment is a very risky one. Germs will pass un- 

 wetted and unscathed through sulphuric acid unless the 

 most special care is taken to detain them. I have re- 

 peatedly failed, by repeating Schulze' s experiments, to 

 obtain his results. Others have failed likewise. The air 

 passes in bubbles through the bulbs, and to render the 



