SELECTED PAPERS 



able substrates for life one also encounters chemical compounds that 

 do not naturally occur and owe their origin entirely to the chemist's 

 ingenuity. 



And yet, this is hardly more than a first step in the direction of a 

 sketch of the marvellous capacities of microbial life. How reverently 

 must we bow our heads before the potentialities of cells that manage 

 to synthesize their various and numerous cell constituents from the 

 simple carbon dioxide molecule exclusive of a radiant energy supply, 

 and satisfy their energy requirements at the expense of some strictly 

 inorganic chemical system. Such systems may be composed of mix- 

 tures of oxygen with, as oxidizable component, for example, sulphur, 

 iron, ammonia, or nitrite. A record achievement in this respect is 

 perhaps furnished by the so-called hydrogen bacteria where we ob- 

 serve life being sustained by the simple conversion of hydrogen and 

 oxygen to water. 



Then we must also consider the following facts. The view had long 

 been held that, apart from the green plants which themselves produce 

 oxygen with the aid of solar energy, the presence of free oxygen is a 

 prerequisite for the maintenance of life. Absence of this gas usually 

 causes an early death of the animal organism. Once again it has been 

 the exploration of the microbial world that has liberated life from this 

 limitation. Pasteur discovered the phenomenon of what he pithily 

 termed 'la vie sans air', with the mighty implication that life is not 

 restricted to the atmosphere or to environments that are in direct 

 contact with it, such as the hydrosphere, but can penetrate into the 

 deeper layers of the lithosphere. 



Compared with the above-mentioned, hardly comprehensible di- 

 versity in physiological types found among micro-organisms, the cor- 

 responding mutual differences encountered among the higher plants 

 and animals become negligible. Hence the microbiologist is always 

 aware of the existence of impressive potencies of life that are all too 

 frequently ignored. In consequence he recognizes that life, in a truly 

 remarkable variety of manifestations, can be found in every locality 

 where systems with potential chemical energy are present. In view of 

 the dynamic nature of hydro- and lithosphere this implies that in 

 special locations populations flourish and decay, to be superseded in 

 the same or adjoining areas by yet different ones. 



After the recognition of the remarkable diversity in microbial metab- 



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