1870.] BRITISH ASSOCIATION. 331 



the flask, the neck of whicli is plugged with cotton-wool, will 

 remain clear for an indefinite time. I have sought in vain for any 

 explanation of these facts, except the obvious one, that the air 

 contains germs competent to give rise to Bacteria, such as those 

 with which the first solution has been knowingly and purposely 

 inoculated, and to the mould Fungi. And I have not yet been 

 able to meet any advocate of Abiogenesis who seriously maintains 

 that the atoms of sugar, tartrate of amonia, yeast-ash and water, 

 under no influence but that of free access of air and the ordinary 

 temperature, re-arrange themselves and give rise to the protoplasm 

 of Bacterium. But the alternative is to admit that these Bacteria 

 arise from germs in the air ; and, if they are thus propagated, the 

 burden of proof, that other like forms are generated in a diiferent 

 manner, must rest with the asserter of that proposition. 



To sum up the effect of this long chain of evidence: — 



It is demonstrable, that a fluid eminently fit for the develope- 

 ment of the lowest forms of life, but which contains neither germs 

 nor any protein compound, gives rise to living things in great 

 abundance, if it is exposed to ordinary air ; while no such develope- 

 ment takesplaceif the air with which it is in contact is mechanically 

 freed from the solid particles, which ordinary float in it, and which 

 may be made visible by appropriate means. 



It is demonstrable, that the great majority of these particles are 

 destructible by heat, and that some of them are germs, or living 

 particles, capable of giving rise to the same form of life as those 

 which appear when the fluid is exposed to unpurified air. 



It is demonstrable, that inoculation of the experimental fluid 

 with a drop of liquid known to contain living particles, gives rise 

 to the same phenomena as exposure to unpurified air. 



And it is further certain that these living particles are so 

 minute that the assumption of their suspension in ordinary air 

 present not the slightest difficulty. On the contrary, considering 

 their lightness and the wide diffusion of the organisms which pro- 

 duce them, it is impossible to conceive that they should not be 

 suspended in the atmosphere in myriads. 



Thus the evidence, direct and indirect, in favour of Biogenesis 

 for all known forms of life must, I think, be admitted to be of 

 sreat weisrht. 



On the other side, the sole assertions worthy of attention are, 

 that hermetically sealed fluids, which have been expo-ed to great 



