HEAT UPON LIVING MAT. TER. 181 
becomes probable, whenever it is made certain that 
Infusoria are generated in solutions in which the 
conditions just mentioned have been complied with. 
We say probable, because their appearance under 
such circumstances would not amount to a proof. 
The absolute proof of spontaneous generation must 
come from the formation of living organisms out of 
inorganic matter. If Infusoria are generated in 
solutions of organic matter, independently of spores 
or germs, the question may be fairly raised whether 
we do not begin the experiment with materials in 
which life already exists, even though this material 
is not in the form of distinct organisms.” Now, 
these last few lines as they at present stand, tend, 
as it appears to me, to convey to the reader very 
erroneous impressions—and yet I am aware that 
views of the same kind are very commonly ex- 
pressed, and seem to exist in an inchoate or half- 
realised form in the minds of many distinguished 
‘persons. It is for this reason, and on account of 
the authority attaching to Professor Wyman’s state- 
ments that I am induced to take notice of this 
particular passage in order to attempt its recti- 
fication. 
In the first place then, under the old term, 
‘spontaneous generation’ are included two processes 
quite distinct from one another—namely, Hetero- 
