CHAPTER VIII. 



ANAEROBIC BACTERIA. 



WHEN Pasteur in 1861 made known to the world that he had dis- 

 covered an organism that could live and multiply without oxygen, 

 the announcement was greeted with astonishment by the scientific 

 world, and was followed by not a few expressions of incredulity. His 

 assertions, however, were completely substantiated, and this opened 

 the way to a new and interesting field of research. Pasteur's organism 

 was described by him as one of the bacteria that were responsible for 

 the butyric-acid fermentation of lactic acid, and named F^ibrion 

 butyrique. As the discovery was made before the days of pure cultures 

 the organism was lost, but it is the same as that which was later 

 described by Prazmowski under the name of Clostridium butyricum. It 

 was found that the presence of oxygen was not only unnecessary, but 

 actually harmful to this organism, for this gas put an end to the 

 motility of the individuals and effectually prevented their growth and 

 multiplication when introduced into a culture of these bacteria. 

 The following simple experiment, first made by Pasteur on Vibrion 

 butyrique, shows the behaviour of such organisms towards oxygen. 

 A drop of the fermenting liquid was placed on a glass slide and 

 examined under the microscope. The bacilli maintained their motility 

 only at the centre of the drop, whereas nearer the edge the motility 

 became less pronounced, and very near and at the edge soon ceased 

 altogether. In consequence of his discovery Pasteur divided micro- 

 organisms into two classes the aerobic, which require, and the 

 anaerobic, which do not require oxygen for their growth and multi- 

 plication. His publication naturally led to further researches on this 

 subject, and it was soon discovered that the anaerobic bacteria were 

 widely distributed and had important parts to play in the economy of 

 nature. They are found in the deeper layers of the soil, in mud, in 



