64 ORIGIN OF LOWEST ORGANISMS. 



the continuance of the ebullition ; whilst immediately 

 after the withdrawal of the heat, the plug was pressed 

 closer, and all the outer unoccupied portion of the 

 tube was rapidly filled up in the same manner. 



Preserved in such a vessel, a specimen of urine 

 remained unchanged ; a hay-infusion also underwent 

 no apparent alteration ; whilst a very strong infusion 

 of turnip became turbid in five days, and ultimately 

 showed a large quantity of deposit.* 



Thus the rules laid down by Pasteur and others 

 are not universal, and therefore, as I have previously 

 pointed out, the explanation which he adduced of the 

 preservation of those particular fluids which remained 

 unchanged is at once rendered doubtful. More espe- 

 cially is there room for doubt on this subject when, as 

 I have found, the result of the experiment can be, 

 within certain limits, predicated beforehand, according 

 to the nature of the fluid employed. If all organisms 

 proceed from pre-existing germs, and these can be 

 filtered from the air by a certain mechanical con- 

 trivance, 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 preserved. Exceptional cases 

 cannot be accounted for on this hypothesis. To 



* These are the only experiments which I have performed 

 with the very long plugs of cotton-wool, though in other previous 

 trials with plugs about 1 2 in. long, I have several times obtained 

 positive results. 



