114 SIMPLER ORGANIC SUBSTANCES 



biochemical organisation of these and other living things." 

 Even those few forms of bacteria which are unable to exist at 

 the expense of organic materials derived from the external 

 medium, such as Thiobacillus thio-oxidans, can nevertheless 

 oxidise their intracellular reserves of polysaccharides during 

 the process of respiration.^* This breakdown is associated 

 with the same enzymic apparatus, the same metabolites of 

 glycolysis, the same vitamins, adenosine triphosphoric acid, 

 etc., which take part in the metabolism of heterotrophs.^^ 

 The inability to assimilate organic substances from the sur- 

 rounding solutions seems, in this case, to be due merely to 

 a peculiar type of permeability of the external membranes 

 of the bacteria in question. The metabolism of all autotrophs 

 is based on a biochemical system for the degradation of 

 organic substances which seems to be extremely primitive 

 and general. The chemosynthetic apparatus would appear 

 to be a secondary, supplementary development which in- 

 increases the complexity of the metabolism. The existence of 

 autotrophic forms within the most systematically diverse 

 groups of micro-organisms also indicates that they have a 

 hereditary relationship to the heterotrophs from which they 

 arose, and that in the course of evolution they have acquired 

 the power to make use of the energy of oxidation of reduced 

 mineral substances. It now seems quite impossible, even 

 from a purely systematic point of view, to suppose that the 

 whole plant and animal kingdoms were derived from the 

 chemosynthetic bacteria. Chemoautotrophy must undoubt- 

 edly be regarded as an offshoot of the evolutionary process.*" 



Even among systematists there is, at present, no unanimity 

 as to which of the existing forms of organism are closest to the 

 prime ancestor of life on the Earth. Many workers think the 

 flagellates are the most primitive (e.g. V. Dogel',*^ L. Kursanov 

 and colleagues,*^ A. Lwoff*^) ; others think the Sarcodina are 

 more primitive (e.g. A. Elenkin,** A. Zakhvatkin,*^ and A. 

 Markevich"**). All are, however, agreed that the obligate 

 heterotrophic organisms which do not require light are 

 the simplest existing organisms. The controversy is about 

 whether these simpler forms arose by degeneration of more 

 complicated ones or Avhether they are themselves nearer to 



