

‘nit 
EXPERIMENTAL METHODS 89 
the flask may be subjected to a calcining heat as it 
passes through the tube. When the flask has become 
cool, its neck is hermetically sealed by the blow-pipe 
flame, so that it will then contain only the previously 
boiled solution in contact with air (at ordinary 
atmospheric pressure) which has been calcined. 
At other times Pasteur has boiled the organic 
solution over the flame, in flasks whose necks have 
been plugged with cotton wool; or else in flasks 
with long, narrow and bent necks. In the first case 
air would only enter the slowly-cooling flask after 
it has been filtered from its impurities by the cotton 
wool; while, in the second form of flask, the air 
which is allowed to re-enter slowly, during gradual 
cooling, is supposed to deposit its impurities in the 
flexures of the long and bent neck. Such methods 
cannot be as safe as the use of hermetically sealed 
vessels. 
Although the presence of air within the closed 
flasks has generally been considered essential, still 
it had been shown by Fray,' even before the time of 
Schwann, that atmospheric air might be replaced 
by other gases such as hydrogen or nitrogen; and 
that even then (with the method of closing the 
vessels at the time in vogue) living organisms were 
subsequently to be met with in the infusions. 
Later, Professor Mantegazza? and Pouchet* showed 
that oxygen gas might be successfully substituted 
for atmospheric air, in experiments which in other 
1“ Fissai sur lorigine des corps organisés et inorganisés,” Paris, 
1821, pp. 5-8. 
2 Giornale dell R. Instituto Lombardo, t. iii. 1851. 
3 Compt. Rend. (1858), t. xlvii. 
