VIII BIOGENESIS AND ABIOGENESIS 249 



of egg), an infusion boiled, and then allowed to 

 come into contact with no air but such as had 

 been filtered through cotton-wool, neither putre- 

 fied, nor fermented, nor developed living forms. 

 It is hard to imagine what the fine sieve formed 

 by the cotton-wool could have stopped except 

 minute solid particles. Still the evidence was 

 incomplete until it had been positively shown, 

 first, that ordinary air does contain such particles ; 

 and, secondly, that filtration through cotton-wool 

 arrests these particles and allows only physically 

 pure air to pass. This demonstration has been 

 furnished within the last year by the remarkable 

 experiments of Professor Tyndall. It has been a 

 common objection of Abiogenists that, if the 

 doctrine of Biogeny is true, the air must be thick 

 with germs ; and they regard this as the height of 

 absurdity. But nature occasionally is exceedingly 

 unreasonable, and Professor Tyndall has proved 

 that this particular absurdity may nevertheless be 

 a reality. He has demonstrated that ordinary air 

 is no better than a sort of stirabout of excessively 

 minute solid particles; that these particles are 

 almost wholly destructible by heat ; and that they 

 are strained off, and the air rendered optically 

 pure, by its being passed through cotton -wool 



It remains yet in the order of logic, though 

 not of history, to show that among these solid 

 destructible particles, there really do exist germs 

 capable of giving rise to the development of living 



