g2 THE EVOLUTION OF LIFE 
seal the flasks actually during ebullition, that is, 
while there was still an out-pouring of steam ; and 
it must be borne in mind that even if the out- 
pouring of steam had ceased for a second before 
the almost capillary orifice of the heated neck of 
the flask had been closed, the neck of the flask 
being at the time in the blow-pipe flame, air could 
only enter through the flame and through the white 
hot capillary orifice itself. It would, in fact, have 
been calcined as in Schwann’s experiment. The 
conditions of the experiment would thus have been 
no less severe, and the only effect would be that 
the vacuum would have been rendered a trifle less 
complete. 
In many of my later experiments with this method 
a slight modification was made. The fluid was boiled 
for a shorter time over the flame, and as soon as 
the flask was hermetically sealed, it was inverted and 
placed in a can of boiling water for the remainder 
of the time during which it was to be _ heated. 
This modification was adopted with the view of 
meeting objections that had been made, and in order 
that all parts of the vessels employed should be more 
effectually brought into contact with boiling water. 
There is only one other principal method—namely 
that employed by Professor Tyndall, and by no 
one else. It was a most complicated and uncertain 
mode of experimentation, which undoubtedly caused 
him much trouble, and led to most contradictory 
results. Some account of it will be given later on 
(Chapter xviii.), when reference will have to be made 
to these experiments. 

