AND THE CAUSES OF FERMENTATION. 127 
Thus it can now be proved, by evidence of a most 
unmistakable nature, that the process of putrefaction 
which invariably occurs in previously boiled putres- 
cible infusions contained in flasks with narrow but 
open necks is not commonly (is, perhaps, only very 
rarely) initiated by living germs or organisms derived 
from the atmosphere; it can also be proved that 
putrefaction and the appearance of swarms of living 
organisms may occur in some boiled fluids when they 
are simply exposed to air which has been filtered 
through a firm plug of cotton-wool or through the 
narrow and bent neck of a flask, to air whose particles. 
have been destroyed by heat, or even in fluids her- 
metically sealed in flasks from which all air has been 
expelled. The evidence in our possession is therefore 
most complete on this part of the subject: it shows 
beyond all doubt, not only that putrefaction may and 
does very frequently occur under conditions in which 
the advent of atmospheric particles, whether living 
or dead, is no longer possible, but also that living 
particles derived from the atmosphere can only be 
very rare and altogether exceptional initiators of the 
putrefaction which invariably occurs in previously 
boiled infusions exposed to the air. 
Again, the evidence which we now possess with 
reference to the influence of heat upon Bacteria, 
Vibriones, and their supposed germs is no less deci- 
