412 FURTHER EVOLUTION 



by Yu. I. Sorokin" for one of the chemoautotrophs, Vibrio 

 desulfuricans. 



According to H. Lees," who has recently done a lot of 

 work on the metabolism of Nitrosomonas, this organism, like 

 other chemoautotrophs, uses the energy derived from the 

 oxidation of inorganic substrates for the assimilation of CO2. 

 In satisfying the internal requirements of the cell, it may 

 use another source of energy, heterotrophic respiration based 

 on the carbohydrates which have been formed. However, 

 this suggestion still requires further experimental amplifica- 

 tion/^ 



It remains obscure why typical ' strict ' chemoautotrophs 

 which have the appropriate catalytic mechanisms cannot 

 work up the exogenous organic substances present in the 

 surrounding medium. Some authors ascribe this to peculiar- 

 ities of the permeability of the cell membranes of these 

 organisms^' but it must be pointed out that very little factual 

 material bearing on this has been collected. In particular, 

 experiments on the nutrition of chemoautotrophs on organic 

 substances have only been carried out for a very limited 

 number of such substances, chiefly glucose, other sugars, 

 amino acids and their polymers. However, this does not 

 show that the organisms tested are absolutely unable to 

 nourish themselves on organic matter. 



In this connection we may note the following interesting 

 fact. We now know that there are organisms which are quite 

 unable to assimilate sugar and other analogous compounds, 

 but which can make good use of such sources of carbon for 

 their nutrition as toluene, phenol, salicylic acid and other 

 typical antiseptics which are very poisonous to all other living 

 things. The literature contains accounts of curious situations 

 in which attempts to sterilise soil with toluene, which is 

 commonly used for this purpose, did not bring about destruc- 

 tion of the microflora, but, instead, the greater proliferation 

 of some members of it.^® These so-called ' cyclists ' have been 

 studied in detail by V. O. Tauson in particular." He isolated 

 them from the soil of petroleum-bearing regions which con- 

 tained a considerable number of bacteria and other organisms 

 which could break down both petroleum and various fractions 

 of it, kerosene, fuel oil, paraffin, lubricating oil, etc. The 



