[47] When infusions have been employed, these have all been made as strong as possible, and have been filtered before use. _Warm_ water has been added in quantity just sufficient to cover the substance to be infused (cut into very small pieces), and the mixture has then been kept at a temperature of from 110°–130° F. for three or four hours. FIRST SET OF EXPERIMENTS (I.–XV.). _a. Fluid exposed to Air in a Flask with a short Open Neck._ *No. I.--Urine* in twenty-four hours was still clear and free from deposit. In forty-four hours the fluid was very slightly turbid, and on microscopical examination _Bacteria_ and _Torulæ_ were found, though not in very great abundance. In sixty-eight hours the fluid was quite turbid. *No. II.--Hay Infusion* in twenty-four hours was still clear. In forty-four hours the fluid was very turbid, and a drop on examination showed multitudes of _Bacteria_ of different kinds, exhibiting languid movements. In sixty-eight hours the turbidity had become much more marked, and there was also a certain amount of sediment. *No. III.--Turnip Infusion* in twenty-four hours showed a very slight degree of turbidity. A drop examined microscopically revealed a number of very minute, but very active, _Bacteria_. In forty-four hours the turbidity had become very well marked. _b. Fluid in contact with Ordinary Air and its Particles; Neck of Flask Sealed after the Fluid had become Cold._ *No. IV.--Urine* remained quite bright and clear during the fifteen days in which it was kept under observation in the water-bath.[48] *No. V.--Hay Infusion* after forty-four hours showed a well-marked turbidity. In sixty-eight hours there was an increase in the amount of turbidity, and also some sediment. During the next forty-eight hours turbidity and sediment gradually increased, whilst the colour of the fluid (originally that of port wine) became several shades lighter. Except that it grew still lighter in colour, and that the amount of sediment increased, it underwent no further obvious change during the fifteen days in which it remained in the bath.[48] *No. VI.--Turnip Infusion* underwent no change during the fifteen days in which it was kept in the bath under observation.[48] _c. Fluid in a Flask with a Neck two feet long, and having Eight acute Flexures._ *No. VII.--Urine* remained quite bright and clear during the fifteen days in which it was kept under observation in the water-bath.[48] [48] Flask still in my possession, unopened. *No. VIII.--Hay Infusion* remained bright and clear for twelve days. On the thirteenth day a very slight (almost inappreciable) sediment was seen, which scarcely underwent any obvious increase during the next eight days, though on the two following days (twenty-second and twenty-third) the turbidity became most obvious: much sediment was deposited, and the fluid assumed a much lighter colour.[49] (On the twenty-second day the temperature of the bath was raised to 100° F., for two or three hours.)