^Appendix. 261 



Schwann, respectively. The first experimenter arranged his flasks 

 with tubes bent at right angles and sealed to the stopper. To 

 these tubes were attached a series of bulbs, which contained on 

 one side anhydrous sulphuric acid and on the other a strong so- 

 lution of caustic potash. Air was then by suction daily drawn 

 into the flasks, passing in through the acid and emerging from the 

 potash side. This process was continued for months (May to 

 September) and no trace of infusoria, confervas or fungi was 

 found in the fluids. Schwann's experiments varied from Schul- 

 tze's in that he passed air in through a series of bent tubes, which 

 were heated up to 600 F. The results, however, were the same, 

 and in both cases it was proven that the air or oxygen had un- 

 dergone no change. Thus it seemed clear that whenever life 

 made its appearance in the infusions in closed flasks it was pro- 

 duced by germs introduced from without, and in the experiments 

 under consideration, the germs in the atmosphere (if there were 

 any) were destroyed by the acid and the calcination. 



These experiments were accepted almost universally as de- 

 monstrative of the incorrectness of the theory of spontaneous 

 generation and it may be said with propriety that within a few 

 years subsequently the question was deemed to have been put to 

 rest for all time. But a rigorous analysis of the evidence shows, 

 as Prof. Huxley has very justly pointed out, that this conclusion 

 is not warrantable. All that the experiments really proved was 

 " that the treatment to which the contents of the flasks had been 

 submitted had destroyed something that was essential to the de- 

 velopment of life. This something might be solid, fluid or gas- 

 eous ; that it consisted of germs remained only a hypothesis ot 

 more or less probability," and, no one, it must be remembered, 

 had ever yet seen the germs. Helmholtz, in 1843, by his experi- 

 ments narrowed this issue by showing that the interposition of a 

 membrane between a putrefying (swarming with life) solution 

 and one that is simple putrescible prevents the development of 

 organisms in the latter. The cause of the development must 

 therefore be something that cannot pass through the membrane. 



But gases and fluids can readily pass through, and hence it fol- 

 ii 



