Taking urine as a fair example of such a fluid, I have found that the statements of M. Pasteur and of Professor Lister are perfectly correct. This fluid may generally remain for an indefinite period in such vessels[45] without becoming turbid, or undergoing any apparent change. The same is generally found to be the case with an infusion of turnip, and occasionally 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 potassæ; 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 microscopical examination, proved to be composed of an aggregation of _Bacteria_, _Vibriones_, and _Leptothrix_ filaments. 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. [45] I have employed flasks of about 1-1/2 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. 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 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.[46] [46] 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 1-1/2 in. long, I have several times obtained positive results.