x.] BIOGENESIS AND ABIOGENESIS. 233 



of the meshes of which depends upon the closeness of 

 the compression of the wool. Now, Schroeder and Dusch 

 found, that, in the case of all the putrefiable materials 

 which they used (except milk and yolk 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 putrefied, 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 stir-about 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. 



But 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 forms in suitable 

 menstrua. This piece of work was done by M. Pasteur 

 in those beautiful researches which will ever render his 

 name famous ; and which, in spite of all attacks upon 

 them, appear to me now, as they did seven years 



