48 
PROFESSOR TYNDALL ON THE OPTICAL DEPORTMENT OF THE 
§ 17. Dr. Bastian’s Experiments. 
The uniform sterility of the boiled infusions described in the foregoing pages, when 
protected from the floating matter of the air, proves that they do not contain germs 
capable of generating life. Dr. Bastian, indeed, affirms that a temperature of 140° 
Fahr. reduces, in all cases, such germs to a state of actual or potential death. But 
even in flasks which have been raised to a temperature of 212°, and hermetically 
sealed, putrefaction, and its associated Bacterial life, do, he alleges, most certainly 
arise ; from which he infers that Bacteria are spontaneously generated. “ We know,” 
he says, “ that boiled turnip- or hay-infusions, exposed to ordinary air, exposed to fil- 
tered air, to calcined air, or shut off altogether from contact with air, are more or 
less prone to swarm with Bacteria and Vibriones in the course of from two to six 
days” *. 
We are here met by a difficulty at the outset. Dr. Bastian’s proof of Bacterial death 
at 140° Fahr. consists solely in the observed fact, that when a certain liquid is heated to 
that temperature no life appears in it afterwards. In another liquid, however, he finds 
that life appears two days after it has been heated to 212°. Instead of concluding logi- 
cally that in the one liquid life is destroyed and in the other not, he chooses to assume 
arbitrarily that 140° Fahr. is the death-temperature for both ; and this being so, the life 
observed in the second liquid figures, in his inference, as a case of spontaneous generation. 
A great deal of Dr. Bastian’s most cogent reasoning rests upon this extraordinary founda- 
tion. Assumptions of this kind guide him in his most serious experiments. He finds, for 
example, that a mineral solution does not develop Bacteria when exposed to the air ; and 
he concludes from this that an organic infusion also may be thus exposed without 
danger of infection. He exposes turnip-juice accordingly, obtains a crop of Bacteria , 
which, in the light of his assumption, are spontaneously generated. Such are the warp 
and woof of some of the weightiest arguments on this question which have been 
addressed by him to the Koyal Society f. 
Granting, then, all that Dr. Bastian alleges regarding his experiments to be correct, 
the logical inference would be very different from his inference. But are his statements 
correct \ This is the really important point ; and to its examination I now address 
myself. 
§ 18. Experiments with Filtered Air. 
A bell-jar containing about 700 cubic inches of air was firmly cemented to a slab of 
wood supported on three legs J. Through the slab passed, air-tight, three large test- 
* Evolution and the Origin of Life, p. 94. 
t Proceedings, vol. xxi. p. 130. 
J Two hoops of sheet iron, with an annular space about an inch wide, were fastened on to the slab of wood. 
The annular space was filled with hot cement, into which the hot bell-jar was pressed. The circular space 
within the smaller hoop was also covered by a layer of cement. 
