232 MICRO-ORGANISMS AND FERMENTATION. 



then hermetically sealed. When he opened them later he 

 found living " infusoria '* in the material, and he naturally 

 argued that they were spontaneously generated, and that the 

 substances liberated during decay had combined again and 

 formed these microscopic forms of life. 



Needham 's experiments were sharply criticised by Spallan- 

 zani in 1765, who proved that if decoctions were maintained 

 for three-quarters of an hour at the boiling point, no living 

 forms were developed until air was admitted. These experi- 

 ments, incidentally, gave a rational basis to the processes of 

 Scheele and Appert. Needham replied that this result could 

 be explained in a perfectly natural way by assuming that the 

 air present in the vessels was so altered in its character by 

 continued heating that it was no longer able to maintain life. 

 Spallanzani was unable to combat this view experimentally, 

 and so the matter remained undecided, and each view had 

 its supporters. The Needham school was supported by the 

 observation of Gay-Lussac that air in hermetically-sealed 

 vessels contained no oxygen. 



No progress was made until the year 1836. From this 

 time on begins a period of rational investigation. Franz 

 Schulze proved for the first time that oxygen does not play 

 the part that had previously been assumed, and his experi- 

 ments also led to the introduction of the first indications of 

 a biological theory alongside the dominant chemical theory. 

 Schulze vigorously boiled a mixture of water and organic 

 matter in a glass flask, and then allowed air to pass through 

 the flask after bubbling through sulphuric acid. This was 

 carried on daily for a long time. The result showed that the 

 contents of the flask could be preserved unaltered for months 

 together, whereas living forms of matter appeared in the de- 

 coction as soon as the vessels were opened and exposed to the 

 access of air. 



At the same time Schwann carried out a similar experiment, 

 with the exception that air was passed through a red-hot 

 tube into the decoction. He obtained identical results. 



But, although these experiments proved that the air 

 present in the flasks contained oxygen, and that living matter 

 was not produced, they proved unconvincing to the supporters 



