PERSISTENCE OF PUTREFACTIVE AND INFECTIVE ORGANISMS. 
193 
infusions are charged all reach their final development at the same moment. Some 
are drier and harder than others, and some, therefore, will be rendered plastic and sen- 
sitive to heat before others. Hence the following procedure. 
Four and twenty small retorts were charged with hay-infusions on the 1st of February, 
and subjected morning and evening to the boiling temperature for one minute. The 
last heating took place on the evening of the 3rd of February. The retort-necks 
had been plugged with cotton-wool; the air within them, however, had not been 
filtered, and there was comparatively little care bestowed on their preparation. 
After the final heating they were abandoned to the temperature of a room kept close to 
90° Fahr. A series of similar retorts charged at the same time with the same infusions 
were boiled continuously for ten minutes, plugged 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 discon- 
tinuous boiling remained permanently brilliant and free from scum. 
On the 1st of February eight pipette-bulbs were charged with two hay-infusions, four 
bulbs being devoted 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 infusions were boiled continuously 
for ten minutes and suspended beside their neighbours. Twelve hours subsequent to 
their first brief heating the eight bulbs were perfectly brilliant, and while in this con- 
dition 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 expe- 
riment was that two days after their preparation the four bulbs which had been boiled 
for ten minutes were found turbid and covered with scum, while two months after 
their preparation the eight bulbs whose periods of boiling added together 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 remaining 
germs can develop themselves into Bacteria they are subjected to another brief period 
of heating. This again kills such germs as are sufficiently near their final develop- 
ment. At each subsequent period of heating the number of living germs is dimi- 
nished, until finally they are completely destroyed. The infusion, if protected from 
external contamination, remains for ever afterwards unchanged, although, when living 
Bacteria , a sprig of hay, or even the dry dust particles of the laboratory are sown in 
it, the sterilized liquid shows its power both of enabling the fully developed organism 
to increase and multiply, and of developing the desiccated Bacterial germ into multi- 
tudinous Bacterial life. 
On the same date an experiment was made with a series of pipette-bulbs, whose 
