CHEMICAL PHENOMENA IN LIFE 



as with oxygen, and with some bacteria it is 

 the same. For other microbes the presence 

 of air is deleterious, as they soon die when 

 brought in contact with a medium containing 

 even only small quantities of oxygen. The 

 possibility of life without oxygen can be shown 

 by the following experiment. A flask is filled 

 with a culture medium of sugar, pepton, and 

 Liebig's extract of meat. This liquid is sterilised 

 by boiling and infected with bacteria from tegu- 

 ments of bean-seeds. A quantity of soluble 

 indigo is added to stain the liquid dark blue. 

 Then the flask is well corked and allowed to remain 

 for one or two days in the incubator at 25 to 30 

 degrees Celsius. After this time we are sure to 

 see the liquid quite colourless, the soluble indigo 

 being reduced by the anaerobic bacteria which 

 develop rapidly and take the oxygen from the 

 indigo. When the bottle is reopened and its con- 

 tents poured slowly out into a dish, we see the 

 liquid immediately colouring greenish, then light 

 blue, and soon dark blue, as it was before. This 

 change is brought about by the reabsorption of 

 oxygen from the air. Such experiments show 

 distinctly that bacteria can grow without more 

 than minute traces of oxygen, and that under 

 such conditions the bacteria are able to draw 

 oxygen from its compounds by reduction. Different 

 results that have been arrived at lead to the con- 

 clusion that enzymes also take part in this process 



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