Aerobiosis and Anaerobiosis ; Light-producing Bacteria ; Marine 

 Bacteria ; Sulphur and Iron Bacteria. 



THE old and now obsolete term ' vital air ' applied to oxygen meant 

 that without it life was impossible. Of all the axioms of physiology, none 

 has ever seemed to be so unassailable as that which asserted the necessity 

 of oxygen to every living thing. It appeared to be a law absolutely 

 without exception that all animals and all plants must ( breathe 1 that is 

 to say, must take up free oxygen in order to oxidise and break up the 

 organic compounds of their food or of their tissues, and thus obtain the 

 energy necessary for the processes of life. Deprivation of air seemed 

 inevitably followed by cessation of life. Here again the study of yeasts 

 and fermentative bacteria has overturned the old views and revolutionized 

 our ideas regarding the chemistry of life. 



In 1861 Pasteur (31) discovered that many zymogenic bacteria could live 

 and even set up active fermentation in the absence of oxygen ; and he gave 

 them for this reason the name of anaerobes. His statements, romantic and 

 improbable as they at first appeared, were soon corroborated, and the 

 general recognition of their accuracy has resulted in the division of the 

 bacteria into two groups, the aerobes and the anaerobes. In the aerobic 

 bacteria the process of respiration is the same as in all ordinary organisms. 

 They absorb oxygen, and with it break up non-nitrogenous bodies such as 

 glycerine or sugar into carbonic acid and water. They are also able, like 

 plants and animals, to assimilate nitrogenous substances such as peptones 

 and amido compounds, although with less gain of energy and less easily 

 than they can carbonaceous bodies. Many of the aerobic bacteria are 

 totally unable to live without oxygen, and when deprived of it die as would 

 a mouse in pure hydrogen. They are exclusive or obligatory aerobes. In 

 rarefied air or in artificial mixtures of gases their vitality is proportional to 

 the amount of oxygen present. Under an air-pump, for instance, they 



