SPONTANEOUS GENERATION. 565 
qually skillful and equally careful, operating in 
places on the same infusion, in the same way, and 
m enters e 
different places on the same infusion, in the same way, 
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 Spallanzaui 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 un wetted 
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 Sch.wa.uu, Kedij as we 
