FIRST HETEROTROPHS AND ANAEROBES 409 



in the time of S. Vinogradskii^" it was suggested in regard 

 to these organisms (as well as to the more pronounced auto- 

 trophs which can develop in purely mineral media) that 

 organic substances not only were not assimilated by them but 

 actually hindered their gi'owth, i.e. were toxic to them. 



This idea had its theoretical basis in the preconceived 

 conviction, which was referred to in Chapter IV, that the 

 first organisms must have been able to make organic materials 

 for themselves because none were present on the Earth before 

 the origin of life. 



For this reason the chemoautotrophs were also regarded 

 as extremely primitive organisms, the organisation of which 

 lacked the chemical mechanisms which enabled all other 

 living things to use organic substances as sources of energy 

 and as immediate structural materials for the synthesis of the 

 components of their protoplasm. 



This idea of the primitiveness of the metabolism of chemo- 

 autotrophs was due to the fact that our knowledge of it was, 

 and to some extent still is, very limited. But the further 

 the study of this field progresses the clearer it becomes that 

 the organisation of the metabolism of chemoautotrophs is 

 very complicated in comparison with that of many other 

 living things. ^^ Their ability to use energy derived from the 

 oxidation of inorganic substances for the synthesis of the 

 components of their protoplasm is not due to the simplicity 

 of their organisation. On the contrary, they manifest a high 

 degree of complexity and integration which could not, by 

 any means, be primary but must have arisen as a result of 

 prolongeci evolution. This is indicated by the fact that the 

 overwhelming majority of chemoautotrophs are markedly or, 

 so to speak, * essentially ' aerobic. The characteristic reactions 

 on which their autotrophy is based take the form of the 

 oxidation of reduced inorganic compounds by molecular 

 oxygen. The catalytic mechanisms underlying these reactions 

 could obviously not have arisen during the period when 

 reducing conditions prevailed on the Earth. They could only 

 have been elaborated secondarily, when the atmosphere of 

 our planet had been considerably enriched with free oxygen. 



It is very characteristic of chemoautotrophs that a more 

 searching investigation of their complicated metabolism 



