4 HISTORICAL. 
isms, nearly allied to the alge. His classification will be found 
in the “‘ Dictionnaire Encyclop. des Sciences Médicales,” art. ‘* Bac- 
téries” (1868). This view is also sustained by the German botanist 
Cohn and is now generally accepted. 
Spallangani, in 1776, endeavored to show by experiment that the 
generally received theory of the spontaneous generation of micro- 
érganisms 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 microérganisms 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 
microérganisms. The same author is entitled to the credit of hav- 
ing first clearly stated the essential relation of the ysast plant— 
Saccharomyces cerevistce—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—7.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 Schréder and Von Dusch (1854) by a 
very simple device which has since proved to ba 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 microdrganisms, and that 
