224 ANIMAL BIOLOGY 



it would only be conceivable for life to survive far below their 

 surface where the temperature is lower. To avoid this and other 

 difficulties it has been suggested that the radiant pressure of light 

 is sufficient to overcome the attraction of gravitation for particles 

 of the extraordinary minuteness of some of the lower forms of life, 

 and that isolated germs might make the journey to the Earth. 

 But on the assumption that an organism were forced out into 

 space by the mechanical pressure of light waves from the sun of 

 the nearest solar system, it would require many thousand years 

 for it to reach the Earth. However, it has been suggested that, 

 owing to the exceedingly low temperature and absence of water 

 vapor which must prevail in cosmic space, there is no reason why 

 spores should lose appreciably more of their germinating power in 

 ten thousand years than in six months. 



Without further discussion, it is apparent that the cosmozoa 

 theory is one which cannot be proved or disproved. It removes the 

 origin of life to a "conveniently inaccessible corner of the universe 

 where its solution is impossible." Although at first thought it 

 seems almost absurd, with its strictly scientific formulation by 

 recent physicists and biologists, and especially in view of our in- 

 creasing knowledge of the powers of life in the latent state, we are 

 justified, perhaps, in seriously wondering whether after all life 

 has ever arisen, whether it may not be as old as matter, and whether 

 its germs, passing from one world to another, may not have de- 

 veloped where they found favorable soil. 



But the majority of biologists undoubtedly would agree that, 

 "knowing what we know, and believing what we believe, as to the 

 part played by evolution in the development of terrestrial matter, 

 we are, without denying the possibility of the existence of life in 

 other parts of the universe, justified in regarding cosmic theories 

 as inherently improbable." Accordingly we may turn to theories 

 which attempt to picture the evolutionary origin of life from the 

 inorganic upon the Earth. 



2. Pfliigers Theory 



Assuming that the Earth was at one time in an incandescent 

 condition, Pfliiger imagines that there arose from this superheated 

 mass a combination of carbon and nitrogen to form the radical 

 cyanogen, CN. This union involves the taking up of a large 

 amount of energy in the form of heat, and therefore cyanogen 



