78 LOUIS PASTEUR 



throughout the fluid were found to become immo- 

 bile near the edges. This is quite the reverse of 

 what often happens with other forms, because it is 

 near the edge that there is the most abundant 

 supply of oxygen. Can it possibly be that oxygen, 

 the great supporter of life, checks the movements 

 of these forms? Ready as always to put his ideas 

 to the test of experiment Pasteur passed a current 

 of air through a flask of liquid containing active 

 vibrios, thus supplying the material with an abun- 

 dance of oxygen. The activities of the vibrios 

 ceased, and the butyric acid fermentation that was 

 going on was brought to a close. Pasteur was thus 

 led to the conception of anaerobic life, or life with- 

 out free oxygen, and the organisms which devel- 

 oped best in a medium devoid of oxygen and whose 

 activities are checked in the presence of this sub- 

 stance he called anaerobes. 



The nature of the changes undergone by a de- 

 composing substance may be determined, therefore, 

 by the amount of oxygen with which it is supplied. 

 If it contains a variety of micro-organisms, then, 

 under conditions of free supply of air, certain or- 

 ganisms that require oxygen will develop and pro- 

 duce their characteristic effects. If, on the other 

 hand, the oxygen supply is limited, the anaerobic 



