SPONTANEOUS GENERATION OF MICROBES 25 



ance of living things in liquids which had been previously 

 heated. 



The well-known French chemist J. L. Gay-Lussac (1778- 

 1850) showed, by means of direct analyses, that oxygen, that 

 is the component of the air which sustains burning and 

 breathing, is absent from vessels containing liquid which had 

 been sealed up after boiling. This confirmed Needham's view. 

 To elucidate the part played by oxygen, Gay-Lussac filled 

 with mercury a glass tube which was closed at one end (a 

 eudiometer) and stood it in a vessel of mercury with the 

 closed end uppermost. A grape was then inserted under the 

 mercury into the tube and crushed with a wire which was 

 introduced through the mercury. The juice which ran out 

 of the grape occupied the upper part of the tube. It remained 

 transparent and apparently completely sterile for a long time. 

 However, after the admission of a bubble of air, the juice 

 quickly began to ferment and to be inhabited by micro- 

 organisms.** 



This experiment, which was later made great use of by the 

 adherents of spontaneous generation, is interesting from the 

 point of view that in it the source of infection was, as we 

 kno^v no^v^ the germs of the micro-organisms which were 

 present on the surface of the mercury, to which neither the 

 experimenter himself nor any of his later interpreters had 

 paid any attention. 



In 1836 the German naturalist T. Schwann made a new test 

 of the significance of oxygen for the spontaneous generation 

 of microbes. He caused a stream of heated air to pass through 

 a glass tube into a vessel containing sterile meat broth and 

 showed that in these circumstances the broth did not putrefy. 

 Hence spontaneous generation did not proceed in the 

 presence of a constantly renewed stream of sterilised air. 

 However, a repetition of this experiment using a liquid 

 containing sugar gave completely different results. In spite 

 of the fact that, according to the author, the methods used 

 in them were exactly the same as those used in the experi- 

 ments with the broth, a mass of living micro-organisms often 

 developed.'*' 



In the same year F. Schulze carried out analogous experi- 

 ments differing only in that the air which was admitted into 



