*No. XXV.--Turnip Infusion + 1/2 gr. of Cheese* in forty-eight hours showed no change, though in seventy-two hours there was a well-marked pellicle, in which some bubbles of gas were engaged. After ninety-six hours the neck of the flask was broken; the fluid was found to be fœtid, and it had an acid re-action. On microscopical examination, a portion of the pellicle was seen to consist of multitudes of _Bacteria_, _Vibriones_, and jointed _Leptothrix_ filaments. *No. XXVI.--Simple Turnip Infusion* remained clear, and showed no appreciable change for seven days. On the eighth day a slight general turbidity of the fluid was noticed. On the ninth, the turbidity was rather more marked, though there was no trace of a pellicle; the neck of the flask having been broken, the fluid was found to be _odourless_ and very faintly acid. On microscopical examination, multitudes of languid _Bacteria_ of medium size were found, and also short monilated chains with from two to ten segments. There were no _Vibriones_, _Leptothrix_ or _Torulæ_.[57] [57] The condition of the fluid, and the nature of its contents, were very similar to that met with in No. XXI. _e. Fluid (in vacuo) in a Flask, Sealed during Ebullition._ *No. XXVII.--Healthy Urine* after twenty-four hours showed no change. After eleven days there was still no apparent change, though on the thirteenth a slight amount of flocculent sediment was noticed. This deposit increased in amount, very slowly, during the next fortnight; though afterwards the fluid seemed to undergo no further change, and did not become generally turbid.[58] [58] Still in my possession, unopened. In all probability the flocculi which formed would be found to be similar in their microscopical, as they certainly were in their naked-eye characters, to those met with in No. XXXV. *No. XXVIII.--Healthy Urine (1/3) and Filtered Turnip Infusion (2/3)* after forty-eight hours showed a very slight turbidity, which, however, became quite marked in another twenty-four hours. *No. XXIX.--Albuminous Urine (1/3) and filtered Turnip Infusion (2/3)* after twenty-four hours, showed a slight turbidity, which became much more marked in forty-eight hours; whilst in seventy-two hours there was a considerable deposit at the bottom of the flask. *No. XXX.--Simple Turnip Infusion* showed no change in forty-eight hours, though in seventy-two hours there was well-marked turbidity. The turbidity and sediment continued to increase for several days, and both were most marked on the tenth day, when the flask was opened. There was an outrush of gas, having an extremely fœtid odour. The fluid had an acid re-action, and when examined microscopically, multitudes of _Bacteria_, _Vibriones_ and _Leptothrix_ filaments were found--the movements of the _Bacteria_ being very languid. FOURTH SET OF EXPERIMENTS (XXXI.–XXXVII.). _b. Fluid in contact with ordinary Air and its Particles; Flask Sealed after the Fluid had become Cold._