THE BEGINNINGS OF IIFE. 1 1 



alteration; whilst a very strong infusion of turnip 

 became turbid in five days, and ultimately showed a 

 large quantity of deposit ^ 



The results not being uniform, the explanation 

 offered by M. Pasteur and others, as to the cause of the 

 preservation of the particular fluids with which they 

 experimented, is at once rendered doubtful. More espe- 

 cially is there room for doubt on this subject when the 

 result of the experiment can be predicated beforehand, 

 within certain limits, as I have found, according to 

 the nature of the fluid employed. If the organisms 

 in these experiments all proceed from pre-existing 

 germs, which can be filtered from the air by a certain 

 mechanical contrivance, then, if it be alleged that 

 it is on account of such filtration that certain boiled 

 fluids do not change, all fluids placed under these 

 conditions ought, on this theory, to be similarly pre- 

 served. Exceptional cases cannot be accounted for on 

 this hypothl^sis. To otliers^ however, who say that 

 organisms are capable of arising de novo^ and that 

 fermentation can be initiated without the agency of 

 living things, the above facts appear quite natural. 

 They think that ♦the more the nitrogenous or protein 

 materials contained in a solution are complex and 

 abundant, the more is the solution fitted to undergo 



^ See Appendix C. p. xxxiii. These are the only experiments which 

 I have perfoi-med with the very long plugs of cotton-wool, though in 

 other previous trials with plugs about i|" long, I have several times 

 obtained positive results. 



