8PONTAMSO US GENERA TION. 565 



mentors equally skillful 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 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 quantities 

 of air, and as oxygen was afterward 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 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 infu- 

 sion to destroy whatever life it might contain, Schulze: 

 sucked daily into his flask air which has 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 success 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 unwetted 

 and unscathed through sulphuric acid unless the most 

 special care is taken to detain them. I have repeatedly 

 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 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 observed, water will be found quite as effect- 

 ual as sulphuric acid. By the aid of an air-pump in a 

 highly infective atmosphere I have thus drawn air for 

 weeks without intermission, first through bulbs containing 

 water, and afterward through vessels containing organic 

 infusions, without any appearance of life. The germs 

 were not killed by the water, but they were effectually in- 

 tercepted, while the objection that the air had been injured 

 by being brought into contact with strongly corrosive 

 substances was avoided. 



The brief paper of Schulze, published in Poggendorf's 

 Annalen for 1836, was followed in 1837 by another short 

 and pregnant communication by Schwanu. Red i, as we, 



