184 THE FLOATING-MATTER OF THE AIR. 



After boiling they were removed, permitted to 

 cool, had their necks broken off by a file, and were 

 afterwards exposed to the temperature of our warm 

 room. It may be remarked that the infusion gradually 

 deepened in colour from the 15-minute period, where 

 the colouring was hardly sensible, to the 2-hour period, 

 where the colouring became deep yellow. The effect 

 was doubtless due to the oxidation of the infusion, 

 which, notwithstanding the colour, was in all cases 

 highly transparent. 



Two days after their preparation, every tube of the 

 series had become turbid and had begun to cover itself 

 with scum. 



On March the 6th the periods of boiling were pro- 

 longed with a fresh infusion. Two groups of tubes 

 were, on that day, exposed to boiling water for the fol- 

 lowing times : — 



1st group 180 minutes. 



2nd „ 240 „ 



On the 8th of March all the members of the 

 first group were turbid and covered with scum. The 

 second group was completely sterilized. This latter 

 result is quite in accordance with the experiments made 

 on the 27th of January. Turnip-infusion was then 

 boiled for periods varying from 220 minutes to 305 

 minutes, complete sterilization being in all cases the 

 consequence. These results were subsequently checked 

 by a continuous series of experiments extending over 

 periods of boiling varying from one to six hours. Up 

 to three hours the infusion resisted sterilization ; but 

 when the periods of boiling were prolonged to four, 

 five, and six hours respectively, all the bulbs became 

 permanently barren. The liquid continued in the 

 highest degree transparent, and in colour a brilliant 

 orange-brown. 



