32 
PROFESSOR TYNDALL ON THE OPTICAL DEPORTMENT OF THE 
§ 4. Mutton- Infusion. 
A case was constructed to contain six test-tubes. It, like the others, had a front 
of glass, side windows, and a back door. Its capacity was 857 cubic inches. It was 
sealed up on the 21st of September, and found free from floating matter on the 24th. 
Lean mutton, cut into small pieces, was digested for four hours in water of a tempera- 
ture of 120° F. The infusion was then carefully filtered, and introduced into the six 
test-tubes by a pipette which was never removed from the case. 
The mutton-juice was of a fine ruby colour ; but on boiling, its albumen was preci- 
pitated, subsequently sank, and carried the colouring-matter with it. The supernatant 
liquid was perfectly clear. The frothing was considerable when the boiling began. 
Beside this case was placed a stand containing six test-tubes filled with the same infu- 
sion, but exposed to the common air. 
On the 27th all the outside flasks were perceptibly turbid; on the 28th they were 
found well filled with Bacteria, which on the 30th had increased to astonishing swarms. 
On the 15th of October the tubes were again examined, and found charged with undi- 
minished life. They remained thus “ putrid ” until the 14th of November. 
During the whole of this time the infusion in contact with the moteless air of the 
chamber remained as clear as distilled water. 
On the 14th of November I infected one of the clear tubes by introducing into it 
through the pipette a few drops of mutton-infusion which had been prepared and 
exposed upon the 12th of November, and which two days had sufficed to render turbid. 
On the 15 th the inoculated infusion showed signs of turbidity, and on the 16 th putre- 
faction had actively set in, the liquid being thickly muddy and full of life. 
With a moteless chamber and three tubes, experiments were subsequently made on 
a second infusion of mutton. In this case, however, the infusion was boiled, its albu- 
men was precipitated, and removed by filtration prior to its introduction into the 
chamber. The pellucid liquid was introduced on the 1st of October, boiled for five 
minutes in the brine-bath, and abandoned to the air of the case. A series of exposed 
tubes containing the same infusion, similarly treated, was placed beside the protected 
ones. On the 4th all the outside tubes were muddy and swarming with Bacteria. 
Schroeter and Cohn have shown that different colours are produced by different kinds of 
Bacteria. In the three exposed tubes here referred to a yellow-green pigment was 
developed. 
Up to the present date , or for more than three months after its preparation, the infusion , 
considerably diminished by evaporation , remains in all the protected tubes as clear as 
at first. 
§ 5. Beef Infusion. 
A beef-steak, after having its fat removed, was cut up into small pieces, and digested 
for three hours at a temperature of 120° F. The liquid was then poured off, boiled, and 
filtered. It was as clear and colourless as pure water. On the 4th of October it was 
