no SIMPLER ORGANIC SUBSTANCES 



In 1887 and later S. VinogradskiP (Winogradsky) discovered 

 another source, likewise biogenic, for formation of organic 

 substances on the Earth. This is the so-called ' chemo- 

 synthesis '. Vinogradskii established the natural occurrence 

 of a special physiological category of bacteria, which can 

 synthesise the organic substances of their own bodies, using 

 carbon dioxide as their source of carbon, in darkness and 

 quite independently of light. This they do by making use 

 of energy obtained by bringing about the oxidation of vari- 

 ous mineral substances — some of the more reduced com- 

 pounds of sulphur, iron or nitrogen.^" 



Nevertheless, detailed quantitative estimates of the vari- 

 ous ' nutritional chains ' or attempts at ascertaining overall 

 production of organic substances for the whole surface of the 

 Earth have been made in years gone by^^ and more recently. ^^ 

 All these lead to the conclusion that photosynthesis by green 

 plants is by far the most important source of organic sub- 

 stances for the living beings which at present inhabit the 

 Earth. 



Moreover, photosynthesis has also been responsible for 

 the development of various formations such as coal, which 

 might appear, at first sight, to be mineral in nature. Chemical 

 investigation of organic substances entering into the com- 

 position of coal (particularly lignin), geological study of its 

 distribution in the crust of the Earth and palaeontological 

 study of the numerous fossils obtained from it all agree in 

 pointing to a biogenic origin. The various coals are seen to 

 be derived by far-reaching decomposition and alteration of 

 what was originally mainly residues of plants. These became 

 buried in the crust of the Earth, being subjected at first to 

 the action of micro-organisms and later to high temperature 

 and pressure from the surrounding strata. ^^ 



The biogenic origin of petroleum is more controversial. 

 From the time of M. Berthelot^^ and D. Mendeleev^^ up to 

 the present there has been a lively scientific discussion of this 

 problem. However, most of the authoritative chemists and 

 geologists who have been concerned with this problem (see, 

 for example, C. Engler," A. Arkhangel'skii," V. Ver- 

 nadskii,^* N. Zelinskii,^^ G. Stadnikov,'" I. Gubkin^^^ and 

 others) consider that there is no doubt at all that at least the 



