HISTORICAL. 5 



air passed through such a filter does not cause the fermentation of 

 boiled organic liquids. 



The experiments of Pasteur and of Hoffman, made a few years 

 later, showed that even without a cotton filter, when the neck of the 

 flask containing the boiled liquid is long drawn out and turned down- 

 ward, the contents may be preserved indefinitely without change. 

 In this case suspended particles do not reach the interior of the flask, 

 as there is no current of air to carry them upward through its long- 

 drawn-out neck, and they are prevented by the force of gravity from 

 ascending. 



Tyndall showed at a later date that in a closed chamber, in which 

 the air is not disturbed by currents, all suspended particles settle to 

 the floor of the chamber, leaving the air optically pure, as is proved 

 by passing a beam of light through such a chamber. 



Notwithstanding the fact that the experimenters mentioned had 

 succeeded in keeping boiled organic liquids sterile in flasks to which 

 the oxygen of the air had free access, the question of the possibility 

 of spontaneous generation heterogenesis still remained unsettled, 

 inasmuch as occasionally a development of bacterial organisms did 

 occur in such boiled liquids. 



This fact was explained by Pasteur (1860), who showed that the 

 generally received idea that the temperature of boiling water must 

 destroy all living organisms was a mistaken one, and that, especially 

 in alkaline liquids, a higher temperature was required to insure ster- 

 ilization. His experiments showed that a temperature of 110 to 

 112 C. (230 to 233.6 F.), which he obtained by boiling under a 

 pressure of one and a half atmospheres, was sufficient in every case. 

 These experiments, which have been repeated by numerous investi- 

 gators since, settled the spontaneous-generation controversy ; and it 

 is now generally admitted that no development of microorganisms 

 occurs in organic liquids, and no processes of putrefaction or fermen- 

 tation occur in such liquids, when they are completely sterilized and 

 guarded against the entrance of living germs from without. 



Pasteur, at a later date (1865) showed that the atmospheric or- 

 ganisms which resist the boiling temperature are in fact reproduc- 

 tive bodies, or spores, which he described under the name of " corpus- 

 cles ovoides " or " corpuscles brillants." Spores had been previously 

 seen by Perty (1852) and Robin (1853), but it was not until 1876 that 

 the development of these reproductive bodies was studied with care 

 by Cohn and by Koch. The last-named observer determined the 

 conditions under which spores are formed by the anthrax bacillus. 

 Five years later (1881) Koch published his valuable researches relat- 

 ing to the resisting power of anthrax spores to heat and to chemical 

 agents. 



