THE BEGINNINGS OF LIFE. 379 



M. Pasteur approached the solution of the discrepancy 

 in this way. His attention was arrested by the fact 

 that milk was an alkaline fluid, because he afterwards 

 ascertained that other alkaline fluids also yielded posi- 

 tive results when submitted to the conditions involved 

 in Schwann's experiments. But having satisfied him- 

 self of this, it was necessary for M. Pasteur to offer some 

 explanation, if he was not prepared to yield his assent to 

 the doctrine which he had formerly rejected. He soon 

 found, truly enough, that the mere alkalinity or acidity 

 of the solution was a matter of great importance in 

 these experiments; he ascertained, for instance, that 

 his sweetened yeast- water, naturally a faintly acid fluid, 

 was always unproductive when submitted to Schwann's 

 conditions unaltered, though it was, on the contrary, 

 always productive if it had previously been rendered 

 neutral or slightly alkaline by the addition of a little 

 carbonate of lime. Facts of this kind were observed so 

 frequently as to make him come to the conclusion that 

 whilst acid solutions were never productive in Schwann's 

 apparatus, any neutral or alkaline fluids might be, if 

 they were otherwise suitable for such experiments. 

 Then came the question as to how this was to be 

 explained. 



It should be remembered that M. Pasteur was en- 

 gaged in investigating the problem of the mode of 

 origin of certain low organisms in organic fluids, con- 

 cerning which so much controversy had taken place. 

 In this controversy hitherto, it had been contended on 



