42 
PROFESSOR TYNDALL ON THE OPTICAL DEPORTMENT OF THE 
after the floating matter had subsided, infusions of hay and turnip were introduced. 
Dipping into each test-tube were two tinned copper wires, connected below by a spiral 
of platinum wire. The arrangement is represented in fig. 4. The copper wires ( cd ) 
passed through the case, and were connected with a voltaic battery outside. 
The spiral was heated by the current. After a few minutes ebullition set 
in, and was continued for five minutes in each tube. Two other tubes 
containing the same infusions were boiled in the same way, and afterwards 
hung on outside the case containing the two protected tubes. 
In a separate case were placed two tubes containing infusions of beef 
and mutton. The arrangement and the treatment were precisely the 
same as those just described in the case of hay and turnip. 
Examined some months subsequently, the exposed tubes of all four 
infusions were found turbid and covered with Penicillium, while all the 
four protected tubes remained unchanged. During the boiling process 
some flocculi detached themselves from the tinned surfaces of the copper wires ; but 
in the protected tubes these have fallen to the bottom, and left the supernatant liquid 
clear. Platinum wires would have been better than tinned copper ones. 
§ 15. Partial Piscussidn of the Pesults. 
Thus by experiments, reiterated in many cases, with urine, mutton, beef, pork, hay, 
turnip, tea, coffee, hops, haddock, sole, salmon, codfish, turbot, mullet, herring, eel 
oyster, whiting, liver, kidney, hare, rabbit, fowl, pheasant, grouse, has the induction been 
established that the power of developing Bacterial life by atmospheric air, and its power 
of scattering light, go hand in hand. We shall immediately examine more closely what 
this means. 
In his published works, Dr. Bastian has frequently dwelt upon the necessity of 
employing strong infusions when investigating the phenomena of spontaneous gene- 
ration. I would therefore recall to mind what has been stated on a previous page, 
that in most of the experiments here described the infusion at starting was strong, and 
that it was permitted to evaporate with extreme slowness until its concentration became 
three or four fold what it had been at starting. Every experiment was thus converted 
into an indefinite number of experiments on infusions of different strengths. Never, in 
my opinion, was the requirement as to concentration more completely fulfilled, and never 
was the reply of Nature to experiment more definite and satisfactory. The temperatures, 
moreover, to which the infusions have been subjected embrace those hitherto found effec- 
tual, extending indeed beyond them in both directions*. They reached from a lower limit 
of 50° to a higher limit of more than 100° Fahr. Still higher temperatures were applied in 
other experiments to be described subsequently. With regard to the number of the infu- 
sions, more than fifty moteless chambers, each with its system of tubes, have been tested. 
There is no shade of uncertainty in any of the results. In every instance we have, within 
the chamber, perfect limpidity and sweetness — without the chamber, putridity and its 
* See Proc. of Roy. Soc. vol. xxi. p. 130, where a temperature of 70° is described as effectual. 
