PERSISTENCE OP PUTREFACTIVE AND INFECTIVE ORGANISMS. 
177 
hermetically sealed above the plugs. Six of them were boiled for 215 minutes, and 
three for 220 minutes. They were one and all permanently sterilized ; but, like the 
turnip, all of them were open to infection by fresh hay, dry dust, or living Bacteria. 
The specific gravity of the melon-infusion was 1008. 
§ 17. Further Experiments on the Resistance-limit of Germs to the Boiling Temperature. 
The amount of boiling which turnip-infusion failed to withstand is shown by some of 
the foregoing experiments but to determine the limit of its resistance we must begin 
with shorter periods. On the 1st of March, therefore, eight groups of pipette-bulbs 
were charged with turnip -infusion which had been prepared in an atmosphere purposely 
infected with the germs of old Heathfield hay. In every case, moreover, a sprig of the 
same hay was placed in the air above the infusion. The bulbs had their necks plugged 
with cotton-wool, and were hermetically sealed above the plug. In this condition the 
respective groups were boiled for the following times : — 
1st group .... 
. . . . 15 minutes. 
2nd „ .... 
.... 30 
59 
3rd „ .... 
.... 45 
55 
4th „ .... 
.... 60 
55 
5th „ .... 
.... 75 
55 
6th „ .... 
.... 90 
55 
7th „ .... 
.... 105 
55 
8th „ .... 
.... 120 
55 
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 prolonged with a fresh infusion. Two 
groups of tubes were, on that day, exposed to boiling water for the following 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 
