198 THE FLOATING-MATTER OF THE AIR. 



liquid — a proof necessary to the argument, and admit- 

 ting of no question, being thus offered to the reader. 



On the 22nd of February four groups of bulbs were 

 charged as above described with the same two infusions, 

 and the periods of boiling prolonged as follows : — 



1st group 90 minutes. 



2nd „ 120 „ 



8rd „ 180 



}f 



4th „ 240 



As in the last case, neutral and acid infusions of 

 each kind of hay were operated on. This was the re- 

 sult: — On the evening of the 23rd, that is to say, 24 

 hours after their preparation, every one of these bulbs 

 disclosed to the practised eye that organisms existed 

 within it. At 2 p.m. on the 24th they all swarmed 

 with life. The old Heathfield bulbs, both acid and 

 neutral, were turbid and covered with scum, the very 

 weakly-acid infusions being indistinguishable in appear- 

 ance from the neutral ones. In the case of the 

 Guildford infusion, however, the scum of the neutral 

 infusions was richer and heavier than that on the acid 

 ones. 



Four hours mark the limit to which the boiling was 

 carried in these experiments. On the 27th of February 

 the periods of boiling were still further prolonged. 

 Four groups of bulbs charged with infusions of the 

 same two kinds of hay, both acid and neutral, were on 

 that day boiled for the following times : — 



1st group 300 minutes. 



2nd „ 360 „ 



3rd „ 420 „ 



4tli „ 480 „ 



I had previously boiled infusions of old Heathfield, 

 old London, and old Colchester hay for 5 hours, and 



