28 THEORIES OF SPONTANEOUS GENERATION 



now that under such experimental conditions the appearance 

 of infusoria was simply due to their germs always having 

 reached the original solution from the surface of the hay. 

 This may easily be demonstrated nowadays by direct observa- 

 tion. Pouchet's statement that spontaneous generation of 

 infusoria occurred in his infusions sounds quite unjustified 

 and even ridiculous in the light of present-day knowledge. 

 However, Pouchet's work made a great impression on his 

 contemporaries. 



The work of Pasteur. 



The French Academy of Sciences awarded a prize to who- 

 ever, by means of accurate and convincing experiments, 

 should cast light on the question of the primary origin of 

 living creatures. This prize was awarded to Louis Pasteur^* 

 who, in 1862, published his work on spontaneous generation 

 in which, by a series of conclusive experiments, he demons- 

 trated the impossibility of the formation of micro-organisms 

 from various infusions and solutions of organic substances. 

 Pasteur was successful in doing this only because he left the 

 beaten track of blind empiricism and approached the whole 

 problem broadly in his experiments. He also gave a rational 

 analysis of all earlier experiments and explained the mistakes 

 of those who carried them out. First of all Pasteur cleared 

 up the question of the presence of micro-organisms in the 

 air which, as we have seen above, was considered to be one 

 of their chief origins. The partisans of spontaneous genera- 

 tion, Pouchet in particular, repeatedly expressed doubts as to 

 whether germs of life were really present in air and de- 

 manded a demonstration of the ' infinite mass of micro- 

 organisms ' which are present in the air. 



Pasteur solved this problem by a very simple method. 

 Using an aspirator he drew air through a tube into which a 

 plug of gun cotton had been inserted. As Schroder and 

 Dusch had already shown, all the smallest particles are 

 retained by the cotton and remain in the tube. The current 

 of air was maintained for 24 hours and the plug with the 

 dust which had been caught in it was removed and dissolved 

 in a mixture of alcohol and ether. At this stage all the solid 



