34 
PROFESSOR TYNDALL ON THE OPTICAL DEPORTMENT OP THE 
maintained during the time of digestion, and the time it was to be maintained* were 
scrupulously adhered to. Thus the turnip was cut into thin slices, and digested for four 
hours in a beaker of water immersed in a water-bath kept at a temperature close to 
120° Fahr. The infusion was then carefully filtered, introduced through a pipette 
into its case, and boiled there for five minutes. Six protected test-tubes were charged 
with the infusion on the 24th of September, while six other tubes were placed on a stand 
outside, and exposed to the common air of the laboratory. 
On the 27th the exposed tubes were distinctly turbid, and on microscopic examina- 
tion were found peopled with Bacteria. The protected tubes, on the contrary, were 
perfectly clear. A little distilled water had been added to one of the outer tubes. The 
germinal matter, whatever it may be, must have been copious in the water ; for the tube 
to which it was added far exceeded the other two in the rapidity of life-development. 
On the 30th this tube contained Bacteria in swarms, of small size, but of astonishing 
activity. The other tubes also were fairly charged with organisms, larger and more 
languid, but not at all so numerous as in the watered tube. On the 5th of October 
some of the exposed tubes began to clear ; as if the Bacteria had died through lack 
of nutriment, and were falling as a thick sediment to the bottom. 
During these changes the protected tubes were visibly unaltered, the liguid within every 
one of them remaining as clear as it had been on the day of its introduction. 
In this instance I was specially anxious to verify the result by repetition. Two other 
cases were therefore fitted up to contain three tubes each, and instead of a door a 
movable panel was placed at the back. After two or three days’ rest both cases were 
found free from floating matter, and on the 1st of October the turnip-infusion was intro- 
duced, and boiled for five minutes in a bath of brine. 
In the former experiment the temperature of digestion was maintained by keeping 
the beaker containing the turnip in a bath of warm water. In the present instance 
the turnip was sliced in a dish and placed before a fire. An occult but efficient power 
like that already ascribed to the actinic raysf, might, I thought, be ascribed to radiant 
heat, and I therefore copied to the letter the mode of digesting pursued by Dr. Bastiajst. 
Adjacent to the closed cases was placed a series of three exposed tubes, containing a 
liquid prepared in precisely the same way. On the 4th of October the exposed tubes were 
all turbid, and swarmed with Bacteria. In two of the tubes they were distinctly more 
numerous and lively than in the third. Such differences between sensibly conterminous 
tubes, containing the same infusion, are frequent. On the 9th, moreover, the two most 
actively charged tubes were in part crowned by beautiful tufts of mould. This expanded 
gradually until it covered the entire surface with a thick tough layer, which must have 
seriously intercepted the oxygen said to be necessary to Bacterial life. The Bacteria 
lost their translatory power, fell to the bottom, and left the liquid between them and 
the superficial layer clear. 
* Beginnings of Life, vol. i. p. 357, note. 
t Nature, vol. iii. p. 247. 
