PERSISTENCE OF PUTREFACTIVE AND INFECTIVE ORGANISMS. 
187 
of life was, I doubt not, due to stray germs of exceptional resisting power, which main- 
tained themselves unscathed in the infusions after their fellows had been destroyed. 
By multiplied experiments of a similar character executed subsequently, and fortified 
by others made in a different way, all doubts as to the real ordeal to which the germs 
had been exposed were set at rest. A flood of light, moreover, was thrown upon the 
difficulties recorded in the foregoing pages. Prior to the introduction into our labo- 
ratory of the particular samples of desiccated hay whose adherent germs had manifested 
such extraordinary powers of resistance, infusions of all kinds, even those of hay itself, 
were sterilized with ease and certainty. But the old London, the old Heathfield, the 
Guildford, and the old Colchester hay brought a plague into our atmosphere, and thus 
the infusions of other substances, some samples of hay included, became the victims of a 
pest entirely foreign to themselves. The failure to sterilize cucumber, turnip, beetroot, 
artichoke, melon, beef, mutton, haddock, herring, sole, was plainly due to the fact that 
their infusions had been prepared in an atmosphere, or brought into contact with vessels, 
contaminated with germs which have been here shown capable of resisting 240 minutes’ 
boiling. It is obvious from all this that to speak of an infusion being rendered barren 
by such or such a temperature, is simply to use words without definite meaning ; because 
the temperature at which any infusion is sterilized depends upon the character and 
condition of the germs which find access to it. The death-temperature, for example, 
may be more than three hours in London and less than three minutes at Kew*. 
I may cite here two conspicuous illustrations of the infective energy of those desiccated 
hay-germs in two infusions which, under ordinary atmospheric conditions, are very easily 
sterilized. On the 30th of March five pipette-bulbs were charged with clear beef- 
infusion and boiled for the following times : — 
1st bulb .... 
2nd „ .... 
.... 120 „ 
3rd „ .... 
.... 180 „ 
4th „ .... 
.... 240 „ 
5th „ .... 
.... 300 „ 
After cooling, the sealed ends were broken off, the air being admitted through cotton- 
wool plugs. Every one of these bulbs became charged with organisms. In the shed, 
eight yards off, this beef-infusion was, as already reported, sterilized by five minutes’ 
boiling. 
Precisely the same experiment was made on March 30 with pellucid mutton-infusion. 
Not one of the bulbs was sterilized. All of them are at this moment charged with life. 
* I have already described the distribution of Bacterici-ge rms in the air as “Bacterial clouds.” Were our 
vision sufficiently sharpened to see the manner in which such germs are distributed over the surface of a 
meadow, we should not, I am persuaded, find that distribution uniform. We should, in my opinion, find the 
germs grouped in crowds, with comparatively free interspaces, like violets on an alp, or mushrooms in a field. 
It is therefore conceivable that two bunches of hay from the same meadow may differ from each other in 
deportment. 
