MICROBE AND LIFE 



for example, in the sulphur bacteria. During this gradual develop- 

 ment of metabolism to the degree of complexity that we find in 

 present-day cells, more and more accessory systems must have become 

 involved, and this must needs have gone hand in hand with a closer 

 organisation of the cooperating components. Finally there would thus 

 have appeared a complex that exhibits the essential characteristics of 

 a cell. 



Regardless of whether one is inclined to accept the existence of 

 such a period in the evolutionary history of life, and which we may 

 designate as pre-cellium, or prefers different concepts concerning the 

 manner in which the living cell made its appearance on the earth, 

 there will always be occasion for considering the possibility of an 

 evolution of this first perfect living entity. In whatever manner, this 

 cell must have found in the aqueous environments on the earth, i.e., 

 in the proto-solution, the conditions for its development. This raises 

 the question in how far mutations and the continuous changes in the 

 external environment resulting from metabolic activities may have led 

 to the appearance of novel modes of life that could exploit new areas. 



It is exactly the earlier discussed fundamental unity in composition 

 of the most divergent recent cells that lends strong support to this 

 possibility. It will be necessary, however, to remember that a multipli- 

 cation of living entities, whether precellular or cellular, can be postu- 

 lated only if this process can be coupled with energy-yielding processes. 

 Initially the proto-solution contained an abundant supply of organic 

 hydrogen donators and acceptors. As the anaerobic mode of life un- 

 folded more and more, the supplementation of organic matter, pro- 

 duced by the short-wavelength ultraviolet radiation in the upper 

 layers of the oceans, must have lagged behind the utilization of these 

 substances in the deeper layers. 



The interplay between the organic donators and acceptors must 

 eventually have led to the production of carbon dioxide and more or 

 less completely hydrogenated acceptors. These, in turn, might have 

 been used as donators, provided an adequate acceptor was simulta- 

 neously available. In this respect only carbon dioxide can ultimately 

 be considered, and, as we know from the metabolism of the recent 

 methane producing bacteria, it can indeed be converted into the 

 fully hydrogenated form of carbon methane. Meanwhile, the pro- 

 duction of carbon dioxide by the continued dehydrogenation of the 



5*9 



