156 THE FLOATING-MATTER OF THE AIR. 



placed behind it to be seen of a deep red. The acidu- 

 lated-water infusion remained entirely unchanged ; but 

 this is not worth dwelling on, for in this case, even 

 when exposed to the common air, the infusion resisted 

 infection for a considerable time 



In no case was the fatty scum which had been 

 already so frequently observed formed in any one of the 

 tubes. Some change inimical to the particular organ- 

 isms which produce this scum must have been caused by 

 the soaking of the hay. 



Examined microscopically on the 1 8th of November 

 these infusions, I thought, exhibited undoubted evi- 

 dences of Bacterial life. Bacterial forms were unques- 

 tionably there in considerable numbers, more particularly 

 in the sediment at the bottoms of the tubes. Nor do I 

 now see any valid grounds for doubting the presence of 

 life ; but I was warned against drawing too hastily the 

 conclusion which first prompted itself, by boiling an in- 

 fusion swarming with active Bacteria, and submitting 

 the liquid after cooling to microscopic examination. 

 Here also the dead Bacterial forms were preserved, and 

 it was extremely difficult to distinguish their motions,, 

 which were certainly Brownian motions, from those ob- 

 served in the protected infusions of soaked hay. 



The experiment was thought worth repeating. On 

 the 16th of November accordingly chopped bundles of 

 old Heathfield hay and new Heathfield hay, and of old 

 London hay and new London hay, were placed in glass 

 dishes containing distilled water, and were thus soaked 

 until the 18th. They were then moved from the lower 

 laboratory, and taken, with their glass covers, to a dis- 

 tant room at the top of the Eoyal Institution. Here 

 the four specimens of hay were digested for three hours 

 at a temperature of 120'' Fahr. They were filtered, 

 boiled, refiltered, some of them through 100 layers of 



