366 THE EVOLUTION THEORY 



the assumption of spontaneoua generation. It is for me a logical 

 necessity. 



Even about the middle of the nineteenth century there was acute 

 discussion in regard to the occurrence of spontaneous generation. In 

 the French Academy especially Pouchet brought forward arguments 

 in favour of it, and Pasteur against it. Pouchet observed that living 

 organisms made their appearance in infusions of hay and other 

 vegetable material in which any possible living germs had presumably 

 been destroyed by prolonged boiling. Living organisms, Algee, and 

 Infusorians appeared, notwithstanding the fact that the glass bottles 

 in which they were kept were hermetically sealed. But Pasteur 

 showed that the air contains numerous living germs of lowly 

 organisms in its so-called motes, and that, if these were first removed, 

 Pouchet's infusion would not exhibit any signs of life. He caused 

 the air, which was continually passed through the tubes, to stream 

 first along the heated barrel of a gun, and so destroyed these germs, 

 and no organisms were obtained in the infusions. He showed that 

 the air is teeming with germs by an experiment with boiled infusions 

 which were allowed to lie undisturbed for a considerable time in 

 bottles with open necks, one on the roof of the Institute at Paris, the 

 other on the top of the Puy de Dome in Auvergne, which was at that 

 time still the highest mountain in France. In the Parisian experiment, 

 organisms appeared in the bottles in a very few days, while in those 

 exposed to the pure air at the mountain-top none were seen, even 

 after months had elapsed. 



Strangely enough, these and similar experiments were at the time 

 regarded as conclusive proof against the existence of spontaneous 

 generation, though it is obvious enough that the first living being on 

 this earth cannot have sprung from hay, or from any other organic sub- 

 stance, since that would presuppose what we are attempting to explain. 

 After the fiery earth had so far cooled that its outermost layer had 

 hardened to a firm crust, and after water had condensed to a liquid 

 form, there could at first only have been inorganic substances in 

 existence. In order to prove spontaneous generation, therefore, it 

 would be necessary to try to find out from what mingling of inorganic 

 combinations organisms could arise ; to prove that spontaneous 

 generation could never have been possible is out of the question. 



It would be impossible to prove by experiment that spontaneous 

 generation could never have taken place ; because each negative experi- 

 ment would only prove that life does not arise under the conditions 

 of the experiment. But this by no means excludes the possibility that 

 it might arise under other conditions. 



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