SPONTANEOUS GENERATION 311 



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 effectual as sulphuric acid. Bj the aid of an air-pump, 

 in a highly infective atmosphere, I have thus drawn air 

 for weeks without intermission, first through bulbs con- 

 taining water, and afterward through vessels containing 

 organic infusions, without any appearance of life. The 

 germs were not killed by the water, but they were effect- 

 ually intercepted, while the objection that the air had been 

 injured by being brought into contact with strongly cor- 

 rosive 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 Schwann. Eedi, as 

 we have seen, traced the maggots of putrefying flesh to the 

 eggs of flies. But he did not and he could not know the 

 meaning of putrefaction itself. He had not the instru- 

 mental means to inform him that it also is a phenomenon 

 attendant on the development of life. This was first 

 proved in the paper now alluded to. Schwann placed 

 flesh in a flask filled to one-third of its capacity with 

 water, sterilized the flask by boiling, and then supplied 

 it for months with calcined air. Throughout this time 

 there appeared no mould, no infusoria, no putrefaction; 

 the flesh remained unaltered, while the liquid continued 

 as clear as it was immediately after boiling. Schwann 

 then varied his experimental argument, with no altera- 

 tion in the result. His final conclusion was that putrefac- 

 tion is due to decompositions of organic matter attendant 

 on the multiplication therein of minute organisms. These 



