40 
PROFESSOR TYNDALL ON THE OPTICAL DEPORTMENT OF THE 
infusion being exposed on the same day to the ordinary air. The three protected tubes 
remained clear for three months, while in three days the three exposed ones were 
charged with Bacteria. 
Salmon. — The colouring-matter of this fish did not at all affect the infusion ; indeed 
no better example of original freedom from colour or opalescence, and of persistent 
purity in contact with the moteless air, has occurred to me than salmon-infusion. It 
was introduced into a cylindrical case on the 13th of December, where it continued for 
months to show the brilliant transparency exhibited at first. Three unprotected tubes, 
on the other hand, became turbid and covered with mould in a few days. 
Hops. — One tube of this infusion was protected simply by a lamp-glass, corked and 
cemented above and below. Through the lower cork passed the single test-tube, air- 
tight ; while through the upper one passed the pipette and the bent tubes intended to 
connect the outer and the inner air. The infusion was prepared and introduced on the 
28th of October. In a few days the exposed tube was found turbid and covered with 
mould ; the protected tube, on the contrary, remained clear for several months. 
Tea and Coffee. — One tube of each was protected by a lamp-glass similar to that 
employed in the infusion of hops. Both were prepared on the 28th of October, 
exposed tubes being hung up at the same time. The protected tea has remained clear, 
while the exposed tea is turbid and covered with mould. Both the exposed coffee and 
the protected coffee are turbid and covered with mould. 
The remarks already made with regard to the rabbit-infusion apply here. The case 
is one, not for the hasty admission of spontaneous generation, but for further scrutiny. 
I examined the apparatus as it stood. The pipette used to introduce the coffee (and 
this one only of the three employed in these experiments) rested against the outer edge 
of the tube containing the infusion. This had in part evaporated, had been in part 
condensed, and had trickled down the pipette so as to form a small drop at the point 
where pipette and tube touched each other. The drop had virtually washed the outer 
surface of the pipette, carrying with it, in part, such matter as might have attached itself 
to that surface. A portion of this washing-water reaching the infusion was doubtless 
the origin of the life observed. The sure test, however, was the repetition of the 
experiment under conditions which should exclude this source of error. On the 27th 
of December accordingly two tubes protected by lamp-glasses were prepared, two other 
tubes of the infusion being exposed to the air. The former remained clear for months, 
the latter in the same number of days became turbid and covered with Penicillium. 
§ 12. Infusions of Codfish , Turbot, Herring , and Mullet. - 
With a view of causing these experiments on moteless and mote-laden air to run 
parallel with others made with hermetically-sealed tubes, to be described further on, I 
added the fish named in the heading of this section to the other substances examined. 
The mullet was introduced into its case on the 3rd of January. The warm air had, how- 
ever, so acted on the wood of the case, which had been employed in former experiments, 
