26 THEORIES OF SPONTANEOUS GENERATION 



the vessel with the steriHsed liquid was freed from germs, 

 not by heating but by being passed through strong sulphuric 

 acid. The results were the same. However, numerous repeti- 

 tions of Schulze's experiments gave inconsistent results and 

 in some cases micro-organisms appeared in the liquids.^" 

 This, as we now know, depended on the invasion of the 

 liquid by spores which were present in a resistant state in 

 the bubbles of air passing through the sulphuric acid. 



A little later (1853) the Heidelberg professors H. Schroder 

 and T. Dusch simplified the experiment still further by 

 purifying the air by passing it through a layer of sterilised 

 cotton wool which served as an excellent filter, removing all 

 germs of micro-organisms. Thus they were able to free the 

 air from germs while not submitting it to any chemical treat- 

 ment or applying heat to it. In fact, a series of experiments 

 was made by these workers with meat broths, and the wort 

 of beer. These were boiled and then allowed to stand for 

 many weeks without any change occurring. However, milk 

 and meat without water went bad quickly under these condi- 

 tions and became full of micro-organisms.^^ 



Although all the experiments which had been carried out 

 tended to refute the possibility of spontaneous generation, 

 their evidence was not strong enough, in that they were some- 

 times unsuccessful for no demonstrable reason and micro- 

 organisms appeared in the liquid. We now know that this 

 occurred as a result of the accidental introduction of organ- 

 isms owing to some technical fault ; however, contemporary 

 scientists did not see the matter in that light. All these 

 failures, in spite of a known wish to succeed, might easily be 

 interpreted, and were in fact interpreted, as indicating that 

 spontaneous generation, though not universal, could take 

 place under certain circumstances. This opinion was held 

 even by such outstanding investigators as Dumas, Naegeli 

 and a number of other scientists of the middle of the nine- 

 teenth century. 



The conflict of opinion concerning the possibility of the 

 spontaneous generation of micro-organisms attained its great- 

 est naivete in 1859 when F. Pouchet" published a paper in 

 which he tried to prove this possibility experimentally. In 

 his voluminous work, comprising about 700 pages, Pouchet^^ 



