64 
PROFESSOR TYNDALL ON THE OPTICAL DEPORTMENT OF THE 
second record (Map II.) is placed beside the first. The change may be thus described :■ — 
Instead of one, eight of the tubes containing hay-infusion had fallen into uniform mud- 
diness. Nineteen of these had produced Bacterial slime, which had fallen to the bottom, 
Map I. 26th Oct., noon. 
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Map II. 26th Oct., 7 p.m. 
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Clear. 
Mould. Cloudy. 
Muddy. 
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Muddy. 
Cloudy. 
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Slime. 
Slime and mould. 
Clear. 
every tube containing the slime being covered by mould. Three tubes only remained 
clear, but with mould upon their surfaces. The muddy turnip-tubes had increased 
from four to ten ; seven tubes were clouded, while eighteen of them remained clear, with 
here and there a speck of mould on the surface. Of the beef, six were cloudy and one 
thickly muddy, while spots of mould had formed on the majority of the remaining 
tubes. Fifteen hours subsequent to this observation, viz. on the morning of the 27th 
of October, all the tubes containing hay-infusion were smitten, though in different 
degrees, some of them being much more turbid than others. Of the turnip-tubes, three 
only remained unsmitten, and two of these had mould upon their surfaces. Only one 
of the thirty-five beef-infusions remained intact. A change of occupancy, moreover, had 
occurred in the tube which first gave way. Its muddiness remained grey for a day and 
a half, then it changed to bright yellow-green, and it maintained this colour to the end. 
On the evening of the 27th every tube of the hundred was smitten, the majority with 
uniform turbidity, some, however, with mould above and slime below, the intermediate 
liquid being clear. The whole process bore a striking resemblance to the propagation 
of a plague among a population, the attacks being successive and of different degrees of 
virulence. I annex copies of the fourth and seventh maps with their respective dates. 
