2 BACTERIOLOGY. 



their source and mode of origin. Among the lowest 

 forms of animal life known at that time were the 

 maggots found in putrefying meat. It was supposed 

 that they developed from the meat during the pro- 

 cess of putrefaction. The animalcules of von Leeu- 

 wenhoeck too were believed to originate spontane- 

 ously. This theory of spontaneous generation held 

 sway and, although there were many opposed to this 

 doctrine, it was not until nearly a hundred years later 

 that Spallanzani (1769), an Italian, tried by experi- 

 ment to show that micro-organisms could not develop 

 in this way. He took animal matter and mixed it with 

 Expert- water in a flask. After boiling the mixture and seal- 

 proving ing the neck of the flask he found that it could be 



spontane- 



eratkm kept for a long time without putrefying and without 

 incorrect anv micro-organisms developing in it. This experi- 

 ment was subjected to much criticism, however, be- 

 cause the air so essential for the development of life 

 was excluded by sealing the flask. This objection 

 was met by modifying the experiment, first by ad- 

 mitting air that had passed through strong sulphuric 

 acid, and later by filtering the air through cotton 

 used to plug the mouth of the flask. It remained for 

 Pasteur (1860) to settle the question beyond dispute 

 by showing that the entrance of dust into mixtures 

 that had been boiled was sufficient to set up putre- 

 faction on account of the germs carried in with it. 

 So long as the air was filtered free of germs by cot- 

 ton plugs, just so long the mixtures remained free 

 from growth. 



