1870.] BRITISH ASSOCIATION, 329 



ness 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 5^olk of egg), an infusion boiled, and then 

 allowed to come in contact with no air but such as had been filtered 

 through cotton-wool, neither putrified 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 filteration through cotton-wool arrests these par- 

 ticles and allows only physically pure air to pass. This demon- 

 stration has been furnished within the last year by the remark- 

 able experiments of Prof. Tyndall. It has been a common objec- 

 tion 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 un- 

 reasonable, and Prof. 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 exces- 

 sively 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 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 developemcnt 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 ago (' Lectures to Working 

 Men on the Causes of the Phenomena of Organic Nature,' 1863, 

 to be models of acurate experimentation and logical reasoning. 

 He strained air through cotton-wool, and found, as Schroederand 

 Dusch had done, that it contained nothing competent to give rise 

 to the developemcnt of life in fluids highly fitted for that purpose. 

 But the important further links in the chain of evidence added by 

 Pasteur are three. In the first place, he submitted to microscopic 

 examination the cotton-wool which had served as strainer, and 

 found that sundry bodies, clearly recognizable as germs, were 

 among the solid particles strained off. Secondly, he proved that 

 these germs were competent to give rise to living forms by simply 



