ORIGIN OF LOWEST ORGANISMS. 63 



sels * without becoming turbid, or undergoing any 

 apparent change. The same is generally found to 

 be the case with an infusion of turnip, and occasion- 

 ally an infusion of hay may be similarly prevented 

 from undergoing fermentation. On the other hand, if 

 the turnip-solution be neutralized by the addition of 

 a little ammonic carbonate, or liquor potassae ; or, 

 better still, if even half a grain of new cheese be added 

 to the infusion before it is boiled, then I have found 

 that the fluid speedily becomes turbid, owing to the 

 appearance of multitudes of Bacteria. In an infusion 

 to which a fragment of cheese had been added, I have 

 seen a pellicle form in three days, which, on micro- 

 scopical examination, proved to be composed of an 

 aggregation of Bacteria, Vibriones, and Leptothrix fila- 

 ments. A mixture of albuminous urine and turnip- 

 infusion has also rapidly become turbid in a vessel of 

 this kind owing to the appearance of multitudes of 

 Bacteria, and so has a mixture containing one-third 

 of healthy urine with two-thirds of infusion of turnip. 



Other infusions have been boiled for ten minutes in a 

 vessel with a horizontal neck two feet long, into which, 

 during ebullition, a good plug of cotton-wool had been 

 carefully pushed down for a depth of twelve or fourteen 

 inches, and cautiously increased in quantity during 



* I have employed flasks of about I \ oz. in capacity, provided 

 with necks two feet in length. In each case, after the flask has 

 been half filled with the fluid, the neck has been bent eight times 

 at an acute angle. 



