SPONTANEOUS GENERATION. 315 



The argument is now to be clenched by an experi- 

 ment which will remove every residue of doubt as to the 

 ability of the infusions here employed to sustain life. 

 We open the back doors of our sealed chambers, and 

 permit the common air with its floating particles to 

 have access to our tubes. For three months they have 

 remained pellucid and sweet flesh, fish, and vegetable 

 extracts purer than ever cook manufactured. Three 

 days' exposure to the dusty air suffices to render them 

 muddy, fetid, and swarming with infusorial life. The 

 liquids are thus proved, one and all, ready for putre- 

 faction when the contaminating agent is applied. I 

 invite my colleague to reflect on these facts. How will 

 he account for the absolute immunity of a liquid ex- 

 posed for months in a warm room to optically pure 

 air, and its infallible putrefaction in a few days when 

 exposed to dust-laden air? He must, I submit, bow 

 to the conclusions that the dust-particles are the cause 

 of putrefactive life. And unless he accepts the hypo- 

 thesis that these particles, being dead in the air, are 

 in the liquid miraculously kindled into living things, 

 he must conclude that the life we have observed springs 

 from germs or organisms diffused through the atmo- 

 sphere. 



The experiments with hermetically sealed flasks 

 have reached the number of 940. A sample group of 

 130 of them were laid before the Royal Society on 

 January 13, 1876. They were utterly free from life, 

 having been completely sterilised by three minutes' 

 boiling. Special care had been taken that the tempe- 

 ratures to which the flasks were exposed should include 

 those previously alleged to be efficient. The conditions 

 laid down by the heterogenist were accurately copied, 

 but there was no corroboration of his results. Stress 

 was then laid on the question of warmth, thirty degrees 

 50 



