250 BIOGENESIS AND ABICGENESIS vill 



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, 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 

 purpose. But the important further links in the 

 chain of evidence added by Pasteur are three. In 

 the first place he subjected to microscopic exam- 

 ination the cotton-wool which had served as 

 strainer, and found that sundry bodies clearly 

 recognisable 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 effected in the constituents of the air by 

 the wool, by proving that the cotton- wool might 

 be dispensed with altogether, and perfectly free 

 access left between the exterior air and that in the 

 experimental flask. If the neck of the flask is 

 drawn out into a tube and bent downwards ; and 



1 Lectures to Working Mm on the Cam of the Phenomena of 

 Organic Nature, 1863. (See Vol. II. of these Essays.) 



