INTRODUCTION. 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 cerevisie—of alcoholic fermen- 
tation, the process by which sugar is decomposed into 
alcohol and carbonic acid. 
