32 THE EVOLUTION OF MAN. 



because some have supposed that the problem could be 

 solved by means of the crudest experiments. The doctrine 

 of spontaneous generation cannot be experimentally refuted. 

 For each experiment with a negative result merely proves 

 that under the conditions (always very artificial) supplied by 

 us, no organism has been produced from inorganic combina- 

 tions. Neither can the theory of spontaneous generation 

 be experimentally proved unless great difficulties are over- 

 come ; and even if in our own time Monera were produced 

 daily by spontaneous generation — as is very possible — yet 

 the absolute empiric proof of this fact would be extremely 

 difiicult — indeed, in most cases impossible. He, however, 

 who does not assume a spontaneous generation of Monera, 

 in the sense here indicated, to explain the first origin of life 

 upon our earth, has no other resource but to believe in a 

 supernatural miracle ; and this, in fact, is the questionable 

 standpoint still taken by many so-called " exact naturalists," 

 who thus renounce their own reason. 



Sir William Thomson has indeed tried to avoid the 

 necessary hypothesis of spontaneous generation by assuming 

 that the organic inhabitants of our earth originally de- 

 scended from germs which proceeded from the inhabitants 

 of other planets, and which, with fragments of the latter, 

 with meteorites, accidentally fell on to the earth. This 

 hypothesis has met with much applause, and was even 

 supported by Helmholtz. Friederich Zoellner, an acute 

 physicist, has, however, refuted it in his excellent natural- 

 philosophical work "Ueber die Natur der Cometen," a 

 critical book containing most valuable contributions to the 

 history and theory of knowledge.^^' Zoellner has plainly 

 shown that the hypothesis is unscientific in two respects — 



