294 FRAGMENTS OF SCIENCE. 



by the fact, that others in repeating his experiments 

 obtained life where he obtained none. Rather is the 

 refutation strengthened by such differences. 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-established ab- 

 sence in the one case proves that some ingredient for- 

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



Spallanzani's sealed flasks contained but small 

 quantities of air, and as oxygen was afterwards shown 

 to be generally essential to life, it was thought that the 

 absence of life observed by Spallanzani might have 

 been due to the lack of this vitalising gas. To dissi- 

 pate 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 what- 

 ever life it might contain, Schulze sucked daily into his 

 flask air which had passed through a series of bulbs con- 

 taining concentrated sulphuric acid, where all germs 

 of life suspended in the air were supposed to be de- 

 stroyed. From May to August this process was con- 

 tinued without any development of infusorial life. 



Here again the success of Schulze was due to his 

 working in comparatively pure air, but even in such 

 air his experiment is a very risky one. Germs will 

 pass unwetted and unscathed through sulphuric acid 

 unless the most special care is taken to detain them. 

 I have repeatedly failed, by repeating Schulze's experi- 

 ments, to obtain his results. Others have failed like- 

 wise. The air passes in bubbles through the bulbs, and 

 to render the method secure, the passage of the air 

 must be so slow as to cause the whole of its floating 

 matter, even to the very core of each bubble, to touch 

 the surrounding liquid. But if this precaution be ob- 



