118 MICROBES, FERMENTS, AND MOULDS 



on the surface of liquids, or of the organic substances 

 on which they feed. These are termed aerobics, 

 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 anaerobies. 



p n 



Fig. 63. Vibrio rugula in different stagss of development ^anaerobie), 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 aerobie ; while Vibrio rugula 

 (Fig. 63), which lives below the surface of the liquid, 

 below the layer formed by the Bacterium termo, is an 

 anaerobie, 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 aerolde, and the yeast 

 of inferior beer is an anaerobie, etc. Paul Bert regards 



