212 THE FLOATING-MATTER OF THE AIR, 



while boiling, and placed in the same warm room. Two 

 days after their preparation the retorts last mentioned 

 had, without a single exception, given way to turbidity 

 and scum. On the other hand, twelve of the twenty-four 

 retorts which had been subjected for a much shorter 

 period to the discontinuous boiling remained perma- 

 nently brilliant and free from scum. 



On the same 1st of February eight pipette-bulbs were 

 charged with two hay -infusions, four bulbs being de- 

 voted to each. The air above the infusions was the 

 unfiltered air of the laboratory. They were subjected 

 to the temperature of boiling water for a minute ; at the 

 same time four other bulbs containing the same infu- 

 sions were boiled continuously for ten minutes and sus- 

 pended beside their neighbours. Twelve hours subse- 

 quent to their first brief heating the eight bulbs were 

 perfectly brilliant, and while in this condition they were 

 again subjected to the boiling temperature for a minute. 

 On the evening of the same day they were subjected to 

 the boiling temperature for half a minute, and on the 

 following morning the process was repeated. Two 

 additional heatings of the same brief character were 

 resorted to. The result of the whole experiment was 

 that two days after their preparation the four bulbs 

 which had been boiled for ten minutes were found tur- 

 bid and covered with scum, while two months after their 

 preparation the eight bulbs whose periods of boiling 

 added togetlier amounted only to four minutes were 

 perfectly brilliant and free from scum. 



The reason of this procedure is plain. By the first 

 brief application of heat the germs, which are at that 

 moment plastic, are killed ; and before any of the re- 

 maining germs can develop tliemselves into Bacteria 

 they are subjected to another brief period of heating. 

 This again kills such germs as are sufficiently near their 



