EVOLUTION TRACED BIOCHEMICALLY 37 



This organism must have been capable of syntheses which 

 enabled it to hve. It had to depend on the inorganic elements 

 of its environment for these syntheses. Like a number of 

 plancton organisms and bacteria of today, it was capable 

 of combining free atmospheric nitrogen and carbon dioxide 

 to form amino acids, the integral units of the protein mole- 

 cules constituting it, for after a time the primeval atmos- 

 pheric and surface waters of the earth contained no organic 

 compounds which it could assimilate. It could, therefore, 

 live and reproduce itself in an absolutely inorganic world, 

 and its metabohsm, depending wholly on its power to 

 synthesize from inorganic elements its proteins, foreshadowed 

 the diatoms and desmids as well as the Azotobacter 

 of today. The capacity of these to synthesize from carbon 

 dioxide, nitrogen, oxygen, phosphates and sulphates, their 

 organic components is very probably inherited from the 

 protocyte, or if not inherited, then due to a constitution 

 of their complexes which has developed to assimilate the 

 inorganic elements of their environment. 



How minute such an organism must have been can only 

 be inferred from what we know of the minutest organisms 

 of today. These are invisible under the highest power of the 

 microscope, that is, they are less in diameter than o. i micron 

 (a micron being o.ooi of a millimeter) but if they were 

 not transparent they could be revealed with the ultrami- 

 croscope. They can pass through the pores of a Berkefeld 

 filter and are consequently termed "filtrable." One species 

 causes the foot-and-mouth disease, another smallpox, 

 a third rabies, and a fourth the mosaic disease of the tobacco 

 leaf, and there are quite a number of others which are 

 pathogenic. Indeed it is only because of their pathogenic 

 character that we have any knowledge of their existence.. 

 Whether these have a normal habitat of their own and are 

 pathogenic only when they infect animal or vegetable 

 tissues, or whether there are ultramicroscopic organisms 

 which are always non-pathogenic cannot be determined, 

 for there are no methods for demonstrating their existence 

 in the non-pathogenic state. Therefore, it cannot be known 

 whether there are non-pathogenic ultramicroscopic organisms 

 which can and do constitute proteins for their own complexes 



