ATMOSPHERE IN RELATION TO PUTREFACTION AND INFECTION. 
35 
Another difference, pointing to differences in the life of the air, was shown by these 
tubes. The turbidity of the two mould-crowned ones was colourless, exhibiting a grey 
hue. The third tube, the middle one of the three, contained a bright yellow-green 
pigment, and on its surface no trace of mould was to be seen. It never cleared, but 
maintained its turbidity and its Bacterial life for months after the other tubes had 
ceased to show either. It cannot be doubted that the mould-spores fell into this tube 
also, but in the fight for existence the colour-producing Bacteria had the upper hand. 
Six other tubes, similarly exposed, showed the grey muddiness : all of them became 
thickly covered with mould, under which the Bacteria died or passed into a quiescent 
state, fell to the bottom, and left the liquid clear. 
Up to the 13 th of October the purity of the six protected tubes remained unimpaired. 
Here a complementary experiment was made. It remained to be proved that those 
long-dormant clear infusions had undergone no change which interfered with their ability 
to develop and maintain life. On the 13th, therefore, the small panel was removed 
from the back of one of the cases, and with three new pipettes specimens were taken 
from the three tubes within it. The closest search revealed no living thing. The air 
of the laboratory being permitted to diffuse freely into the case, on the day after the 
removal of the panel the test-beam showed the case to be charged with floating matter. 
The access of this matter was the only condition necessary to the production of life ; 
for on the 11th all the tubes were muddy and swarming with Bacteria. 
A similar experiment, subsequently made, revealed to me some of the snares and 
pitfalls which await an incautious worker on this question. The chamber already 
referred to as containing six tubes, filled with turnip-juice, preserved the infusion clear 
for a month. On the 21st of October the back door of the chamber was opened, and 
specimens of the clear infusion were taken out for examination by the microscope. The 
first tube examined showed no signs of life. This result was expected, but I was by no 
means prepared for the deportment of the second tube. Here the exhibition of life was 
monstrously copious. There were numerous globular organisms, which revolved, rotated, 
and quivered in the most extraordinary manner. There were also numbers of lively 
Bacteria darting to and fro. An experimenter who ponders his work and reaches his 
conclusions slowly, cannot immediately relinquish them ; and in the present instance 
some time was required to convince me that no mistake had been made. I could find none*, 
and was prepared to accept the conclusion that in the boiled infusion, despite its clear- 
ness, life had appeared. 
But why, in the protected turnip-infusion, which had been examined on the 13th 
of October, could no trace of life be found 1 In this case perfect transparency was 
accompanied by an utter absence of life. The selfsame action upon light that enabled 
the Bacteria to show themselves in the microscope must, one would think, infallibly 
produce turbidity. Why, moreover, should life be absent from the first member of the 
present group of tubes l I searched this again, and found in it scanty but certain signs 
MDCCCLXXVI. G 
