[53] The filtered infusion of turnip was neutralized by liquor potassæ. The cheese (Cheddar) was new and not in the least mouldy. [54] The fluid itself being somewhat opaque, the first stages of increased turbidity from presence of _Bacteria_ could not be detected. _c. Fluid in a Bent Neck Flask, having Eight acute Flexures._ *No. XVIII.--Simple Turnip Infusion* after forty-eight hours showed no change. It was kept in water-bath for twelve days, and during the whole of this time the fluid remained quite clear. The tube was then broken 1-1/2 inch above the bulb (which was re-immersed in the bath), _leaving the fluid exposed to the air_ through the straight open tube. The fluid at this time was odourless, and its re-action was still faintly acid. The infusion remained thus exposed for six days without undergoing any apparent change. On the eighth day a very slight whitish sediment was noticed, which had increased in quantity by the tenth day, though there was still no trace of general turbidity. On the eleventh day some of the sediment was examined in a drop of the fluid, and it was found to be wholly composed of rather large _Torulæ_ cells--the largest being about 1/3000 in diameter, though all the smaller sizes were abundantly represented. Not a single _Bacterium_ or _Vibrio_ could be detected, and the fluid was still quite odourless.[55] [55] This again is a most instructive experiment when compared with Nos. XVI. and XX., in which portions of the same infusion were employed. The results in No. IX. would lead us to believe that a vegetable infusion which does not ferment, does, nevertheless, undergo some changes in molecular composition, and this notion seems to derive confirmation from the present experiment. Some of the same solution which has been kept for a time (twelve days) from contact with atmospheric particles, subsequently, even when fully exposed to the air, undergoes no apparent change for six days, and then, instead of becoming filled with _Bacteria_, swarms only with _Torulæ_. Yet the infusion in this condition was perfectly capable of nourishing _Bacteria_, as I subsequently proved by inoculating it. Why then was it not inoculated by the living _Bacteria_, with which the air is thought by some to be teeming? *No. XIX.--Neutral Turnip Infusion + 1/2 gr. of Cheese*, showed no perceptible change in twenty-four hours, though in thirty-six hours there was a well-marked pellicle on the surface. When the neck of the flask was broken after seventy-two hours, the fluid was found to be very fœtid, whilst its re-action had become slightly acid. Portions of the pellicle were found to be made up by aggregations of _Bacteria_, _Vibriones_, and an abundance of _Leptothrix_ filaments. The _Bacteria_ all exhibited very languid movements. _e. Fluid (in vacuo) in a Flask which had been Sealed during Ebullition._