118 MICROBES, FERMENTS, AND MOULDS. 
on the surface of liquids, or of the organic substances 
on which they feed. These are termed aérobies, 
or consumers of air. Others, again, can live beneath 
the surface of liquids and in living organisms, or of 
those in process of decomposition, and must neces- 
sarily derive the oxygen necessary for their respira- 
tion from the oxygenated substances in which they 
are found. These are termed anaérobies. 
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a m p n 
Fig. 63.— Vibrio rugula in different stages of development (anaérobie), much enlarged. 
This distinction and the theory on which it relies 
have been introduced into science by Pasteur, and 
they appear to be founded on observed facts. Thus . 
Bacterium termo, which lives on the surface of putre- 
fying liquids, is an aérobie; while Vibrio rugula 
(Fig. 63), which lives below the surface of the liquid, 
below the layer formed by the Bacterium termo, is an 
anaérobie, and derives its oxygen from the water or 
solid matters which are found in it in suspension or 
solution, and even from other microbes. So, again, 
the yeast of superior beer is an aérobie, and the yeast 
of inferior beer is an anaérobie, etc. Paul Bert regards 
