xv.] SPONTANEOUS GENERATION. 361 



and they regard this as the height of absurdity. But 

 Nature occasionally is exceedingly unreasonable, and 

 Professor Tyndall has proved that this -particular ab- 

 surdity may nevertheless be a reality. Pie lias demon- 

 strated that ordinary air is no better tlian 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 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. Pas- 

 teur in those beautiful researches which will ever ren- 

 der his name famous ; and which, in spite of all attacks 

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

 ago 1 , to be models of accurate experimentation and 

 logical reasoning. He strained air through cotton- 

 wool, and found, as Schroeder and Dusch had done, 

 that it contained nothing competent to give rise to the 

 development of life in fluids highly fitted for that pur- 

 pose. But the important further links in the chain of 

 evidence added by Pasteur are three. In the first 

 place he subjected 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 sowing them in a solution fitted 

 for their development. And, thirdly, he showed that 

 the incapacity of air strained through cotton-wool to 

 give rise to life was not due to any occult change af- 



1 " Lectures to Working Men on the Causes of the Phenomena of Organic 

 Nature," 18G3. 



