SPONTANEOUS GENERATION. 581 
inherent life, and placed in contact with air cleansed of its 
visibly suspended matter, has any power to generate life 
anew. 
Remembering then the number and variety of the infu- 
sions employed, and the strictness of our adherence to the 
rules of preparation laid down by the heterogenists them- 
selves; remembering that we have operated upon the very 
substances recommended by them as capable of furnishing, 
even in untrained hands, easy and decisive proofs of spon- 
taneous generation, and that we have added to their sub- 
stances many others of our own if this pretended gener- 
ative power were a realitv, surely it must have manifested 
itself somewhere. Speaking roundly, I should say that in 
such closed chambers at least five hundred chances have 
been given to it, but it has nowhere appeared. 
The argument is now to be clenched by an experiment 
which will remove every residue of doubt as to the ability 
of the infusions here employed to sustain life. We open 
the back doors of our sealed chambers, and permit the 
common air with its floating particles to have access to our 
tubes. For three months they have remained pellucid and 
sweet flesh, fish, and vegetable extracts purer than ever 
cook manufactured. Three days' exposure to the dusty 
air suffices to render them muddy, fetid, and swarming 
with infusorial life. The liquids are thus proved, one and 
all, ready for putrefaction when the contaminating agent 
is applied. I invite my colleague to reflect on these facts. 
How will he account for the absolute immunity of a 
liquid exposed for months in a warm room to optically 
pure air, and its infallible putrefaction in a few days when 
exposed to dust-laden air? He must, I submit, bow to the 
conclusion that the dust-particles are the cause of putre- 
factive life. And unless he accepts the hypothesis that 
these particles, being dead in the air, are in the liquid 
miraculously kindled into living things, he must conclude 
that the life we have observed springs from germs or 
organisms diffused through the atmosphere. 
The experiments with hermetically sealed flasks have 
reached the number of 940. A sample group of 130 of 
them were laid before the Eoyal Society on January 13, 
1876. They were utterly free from life, having been com- 
pletely sterilized by three minutes' boiling. Special care 
had been taken that the temperatures to which the flasks 
