62 PRIMITIVE FORMS OF LIFE 



receive them, reanimate life in places where some premature 

 catastrophe has destroyed it, and enrich it where it already 

 exists by bringing with them greater variety. Thus, on our earth, 

 a fauna extinct at the end of one geological period was replaced 

 by a new one at the beginning of the following epoch, and this 

 phenomenon was repeated over and over again. However, as 

 we said before, the means by which these germs made the 

 journey had still to be discovered. In 1865 Count de Salles- 

 Guyon opined that they must come to us in meteorites or 

 thunderbolts. But this presupposed a disintegrated planet 

 endowed with a tremendous wealth of life. Richter and 

 Cohn preferred the idea of cosmic dust or comets travelling 

 through vast spaces and sowing life as they go. The great 

 physicists Helmholtz and Lord Kelvin accepted this hypothesis, 

 and also the master of the French botanical school, Philippe 

 Van Tieghem. 1 But the germs of life did not come from the 

 planets alone ; they could come also from the stars ; and there- 

 fore they must be considered non-combustible. In 1872, 

 indeed, Preyer did not hesitate to attribute to them this 

 marvellous property. He gives the name of Pyrozoa to creatures 

 born of these germs and able to resist fire. Strange as it may 

 seem, the great physicist, Arrhenius, likewise accepted the 

 idea of insemination by the stars by means of spores analogous 

 to the reproductive cells of algae and mushrooms, which spores 

 possessed tremendous power of resistance to the extreme cold 

 of abyssmal space. These minute germs, he declared, were 

 scattered through space by the centripetal force of the stars, 

 which also threw out such a quantity of minute dust around 

 the sun that it formed what we call its corona, a phenomenon 

 easily visible during total eclipses. Germs of this degree of 

 minuteness mav conceivablv exist, for there are manv microbes 

 that can pass through porcelain and are invisible to the ultra- 

 microscope. However, Paul Becquerel has demonstrated 2 

 that certain ultra-violet rays kill them ; a low temperature 

 certainly augments their power of resistance, but in the end 

 they succumb. This demonstration completely destroys the 

 hypothesis of an extra-planetary insemination, unless we assume 

 that germs coming from other planets possess a constitution 

 peculiar to themselves. However, in the very first place, this 



1 XIII, 982. 2 XVII. 



