ATMOSPHERE IN RELATION TO PUTREFACTION AND INFECTION. 
49 
tubes (A, B, C, fig. 6). Prior to cementing, the tubes 
had been three fourths filled, one with an infusion of hay, 
another with an infusion of turnip, and a third with an 
infusion of mutton. On the 2nd of November the mote- 
laden air was pumped out, air slowly filtered through 
a long tight plug of cotton-wool being allowed to take 
its place. The jar was emptied and refilled until the 
closest scrutiny by a concentrated beam revealed no 
floating matter within it. The infusions were then 
boiled for five minutes, and abandoned to the air of the 
jar. During ebullition a small quantity of the liquid in 
one of the tubes boiled over, and rested upon the interior 
resinous surface at a little distance from the mouths of 
two of the tubes. The germinal matter, it may be re- 
marked, is not readily blown away from such a surface, and it certainly was not removed 
by our feeble current of filtered air. Three similar tubes containing the same infusion 
were placed at the same time beside the protected ones. 
In three days these exposed tubes became turbid and charged with life ; but for three 
weeks the infusions in contact with the filtered air remained perfectly clear. 
At the end of three weeks, that is on the 23rd of November, I desired my assistant to 
renew the air in the bell -jar. He pumped it out, and while permitting fresh air to 
enter through the cotton-wool filter, my attention was directed to a couple of small 
round patches of Penicillium resting on the liquid that had boiled over. I at once 
made the remark that the experiment was a dangerous one, as the entering air would 
probably detach some of the spores of the Penicillium and diffuse them in the bell-jar. 
This was, therefore, filled very slowly, so as to render the disturbance a minimum. 
Next day, however, a tuft of mycelium was observed at the bottom of one of the three 
tubes, namely that containing the hay-infusion. It has by this time grown so as to fill 
a large portion of the tube. For nearly a month longer the two tubes containing the 
turnip- and mutton-infusions maintained their transparency unimpaired. Late in 
December the mutton-infusion, which was in dangerous proximity to the outer mould, 
showed a tuft of Penicillium upon its surface. The beef-infusion continued bright and 
clear for nearly a fortnight longer. The cold winter weather caused me to add a third 
gas-stove to the two which had previously warmed the room where the experiments 
are conducted. The warmth of this stove played upon one side of the bell-jar; and on 
the day after the lighting of the stove, the beef-infusion gave birth to a tuft of myce- 
lium. In this case the small spots of Penicillium might have readily escaped attention ; 
and had they done so we should have had here three cases of “ spontaneous genera- 
tion ” far more striking than many that have been adduced. 
The experiment was subsequently made upon a larger scale. Twelve very large test- 
tubes were caused to pass air-tight through a slab of wood ; the wood was thickly coated 
