INTR OD UCTION. 23 



of organic matter were placed in symmetrically sealed 

 flasks and then boiled the liquids were sterilized ; 

 neither were living organisms found in the solutions, 

 nor did they decompose ; and the infusions remained 

 unchanged for an indefinite period. 



It was objected to these experiments that the high 

 temperature to which the liquids had been subjected so 

 altered them that spontaneous generation could no 

 longer take place. This objection was met by Spall- 

 anzani by cracking one of the flasks and allowing air 

 to enter, when living organisms and decomposition 

 again appeared in the boiled infusions. 



Another objection raised was that in excluding the 

 oxygen of the air by hermetically sealing the flasks the 

 essential condition for the development of fermentation, 

 which required free admission of this gas, was inter- 

 fered with. This objection was then met by Schulze, 

 in 1836, by causing the air admitted to the boiled 

 decomposable liquids to pass through strong sulphuric 

 acid. Air thus robbed of its living organisms did not 

 produce decomposition ; whereas when no such precau- 

 tions were taken with the air admitted the boiled solu- 

 tions quickly fell into putrefaction, and living organ- 

 isms were found to be present. 



Schwann, in 1839, obtained similar results in another 

 way; he deprived the air admitted to his boiled liquids 

 of micro-organisms by passing it through a tube 

 which was heated to a temperature high enough to 

 destroy them. To this investigator is also due the 

 credit of having discovered the specific cause the yeast 

 plant, or saccharomyces cerevisice of alcoholic fermen- 

 tation, the process by which sugar is decomposed into 

 alcohol and carbonic acid. 



