108 THE FLOATING-MATTER OF THE AIR. 



associate, Bacteria. In the rooms without fires the 

 action was slower than in the warmer rooms ; but all 

 the infusions gave way in the end. 



In view of the statements which had been made 

 regarding the scantiness of Bacteria-geTms in the air, 

 observations outside of London would, I thought, be 

 interesting. Accordingly, on the 27th of October, a 

 tube containing an infusion of beef was placed in the 

 hands of Mr. Darwin, who had the kindness to set it in 

 his study at Down and observe its changes. In three 

 days it became cloudy and peopled with Bacteria. The 

 same result was obtained in the open air. Mr. 

 Francis Darwin was good enough to expose an infusion 

 for me in his father's orchard : the weather was cold, 

 and the progress, therefore, slow ; but the tube which 

 had been exposed on the 2nd of November was cloudy 

 and full of Bacteria on the 9th. In Sir John Lubbock's 

 study a similar result was obtained. From Sherwood, 

 near Tunbridge Wells, infusions of fowl and wild duck 

 were returned to me by Mr. Siemens thickly turbid 

 and crowded with Bacteria. From Pembroke Lodge, 

 Eichmond Park, Mr. Eussell returned tubes of turnip, 

 beef, and mutton swarming with life. An infusion 

 of beef exposed at Heathfield Park, Sussex, for a 

 week was returned to me by Miss Hamilton muddy 

 and filled with Bacteria. From Greenwich Hospital 

 Mr. Hirst sent me tubes of beef-, mutton-, and turnip- 

 infusion filled with vigorous Bacteria. Dr. Hooker 

 was good enough to take charge of three sets of tubes 

 at Kew, each set embracing beef, mutton, and turnip. 

 One set was placed in the conservatory, with a tem- 

 perature of 45° to 50°; one in his own study, with a 

 temperature of 54° to 60°; a third set was placed in 

 the orchid-house (the hottest in the gardens), with a 

 temperature of 62° to 75°. 



