4 HISTORICAL. 



isms, nearly allied to the algae. His classification will be found 

 in the " Dictionnaire Encyclop. des Sciences Medicales," art. " Bac- 

 teries " (18G8). This view is also sustained by the German botanist 

 Cohn and is now generally accepted. 



Spallanzani, in 1776, endeavored to show by experiment that the 

 generally received theory of the spontaneous generation of micro- 

 organisms in organic liquids was not true. This he did by boiling 

 putrescible liquids in carefully sealed flasks. The experiment was 

 not always successful, but in a certain number of instances the 

 liquids were sterilized and remained unchanged for an indefinite 

 period. The objection was raised to these experiments that the oxy- 

 gen of the air was excluded by hermetically sealing the flasks, and 

 it was claimed, in accordance with the views of Gay-Lussac, that 

 free admission of this gas was essential for the development of fer- 

 mentation. 



This objection was met by Franz Schulze (1836), who admitted air 

 to boiled putrescible liquids by drawing it through strong sulphuric 

 acid, in which suspended microorganisms were destroyed. He thus 

 demonstrated that boiled solutions, which, when exposed to the air 

 without any precautions, quickly fell into putrefaction, remained un- 

 changed when freely supplied with air which had been passed through 

 an agent capable of quickly destroying all living organisms con- 

 tained in it. 



Schwann (1839) demonstrated the same fact by another method. 

 Air was freely admitted to his boiled liquids through a tube which 

 was heated to a point, which insured the destruction of suspended 

 microorganisms. The same author is entitled to the credit of hav- 

 ing first clearly stated the essential relation of the yeast plant 

 Saccharomyces cerevisice to the process of fermentation in saccha- 

 rine liquids, which results in the formation of alcohol and carbonic 

 acid. 



Helmholtz, in 1843, repeated the experiments of Schwann with 

 calcined air, and arrived at similar results i. e. , he found that the 

 free admission of calcined air to boiled organic infusions did not pro- 

 duce fermentation of any kind. 



It was objected to these experiments that the air, having been 

 subjected to a high temperature, had perhaps undergone some chem- 

 ical change which prevented it from inaugurating processes of fer- 

 mentation. 



This objection was met by Schroder and Von Dusch (1854) by a 

 very simple device which has since proved to be of inestimable value 

 in bacteriological researches. These observers showed that a loose 

 plug of cotton, through which free communication with the external 

 air is maintained, excludes all suspended microorganisms, and that 



