PROFESSOK TYNDALL ON THE OPTICAL DEPORTMENT OF THE 
invaded the distilled water, and made its action rapid. The dilute infusion contained 
multitudes of Bacteria, many motionless, but many moving rapidly about. On the 4th 
of October all the tubes swarmed with Bacteria. They continued muddy till the middle 
of November, when they were employed for experiments on infection. 
Throughout the whole of this time the protected tubes remained unchanged. 
With regard to infection, it may be stated here that the merest speck of a vegetable 
infusion containing Bacteria infects all animal infusions, and vice versd. The bursting 
of a bubble infects an infusion reached by the spray. It is the envelope, and not the 
gas of the bubble, which produces this result. 
Other experiments on hay-infusions, acid, neutral, and alkaline, placed in contact 
with air purified in various ways, yielded the same negative result. 
§ 9. Infusion of Sole. 
The fish was cut up and digested for three hours in water kept at 120° Fahr. On 
the 17th of November it was introduced into a case containing three test-tubes, and 
boiled there for five minutes. Three other tubes hung outside the case were exposed to 
the ordinary laboratory air. 
The three exposed tubes were feebly but distinctly cloudy on the 19th. On the 22nd 
they were all thickly turbid. Scattered spots of Penicillium then appeared on two of 
them, while the third tube, which stood between these two, kept the Penicillium down. 
This central tube contained the pigment-forming Bacteria, which have frequently shown 
a singular power in preventing the development of mould. For nearly two months the 
central tube has successfully withstood this development, while its two neighbours are 
covered by a matted layer of Penicillium. 
During the whole of this time the protected infusion continued as clear and colourless 
as distilled water. 
§ 10. Liver-Infusion. 
On the 10th of November the infusion was prepared by the process of digesting 
already so often described. It was introduced into a case containing three protected 
tubes, and boiled there for five minutes in the brine-bath. Hung on to the chamber at the 
same time were three tubes containing the same infusion, but exposed to the common 
air. On the 13th Bacteria were numerous in the exposed tubes, and soon afterwards 
all three of them became thickly muddy and putrescent. They continued so for 
months. 
The protected tubes, on the contrary , showed throughout a bright yellow liquid , as trans- 
parent as it was on the day of its introduction into the case. 
§ 11. Infusions of Hare, Babbit, Pheasant, and Grouse. 
For the sake of economy, as so many of them were employed, the shape of the cases 
was subsequently varied. The rounded end of a tall glass shade was cut off, so as 
to convert the shade into a hollow cylinder (S, fig. 3), open at both ends. This was set 
