The Origin of Life 17 



seemed probable that there were specific micro-organ- 

 isms which oxidized the ammonia formed in sewage 

 or in the putrefaction of living matter, but the attempts 

 to prove this assumption by raising such a nitrifying 

 micro-organism on one of the usual culture media, all 

 of which contained organic compounds, failed. Led 

 by the results of his observations on sulphur bacteria 

 it occurred to Winogradsky that the presence of organic 

 compounds stood in the way of raising these bacteria, 

 and this idea proved correct. The bacteria oxidizing am- 

 monia to nitrites were grown on the following medium ; 

 1 gm. ammonium sulphate, 1 gm. potassium phosphate, 

 1 gm. magnesium carbonate, to 1 litre of water. From 

 this medium, which is free from sugar and contains 

 only constituents which could exist on the planet before 

 the appearance of life, the nitrifying bacteria were able 

 to form sugars, fatty acids, proteins, and the other 

 specific constituents of living matter. Winogradsky 

 proved, by quantitative determination, that with the 

 nitrification an increase in the amount of carbon com- 

 pounds takes place. "Since this bound carbon in the 

 cultures can have no other source than the CO a and 

 since the process itself can have no other cause than 

 the activity of the nitrifying organism, no other alter- 

 native was left but to ascribe to it the power of assimi- 

 lating C0 2 ." x "Since the oxidation of NH 3 is the 

 only source of chemical energy which the nitrifying 

 1 Winogradsky, loc. cit., p. 163 and ff. 



