292 BIOLOGY AND ITS MAKERS 
ble matter. It is to be noted that the test tubes were not 
corked and consequently that the fluids contained within 
them were freely exposed to the optically pure air within the 
chamber. 
The box was now lifted, and the ends of the tubes extend- 
ing below it were thrust into a bath of boiling oil. This set 
the fluids into a state of boiling, the purpose being to kill 
any germs of life that might be accidentally introduced into 
them in the course of their conveyance to the test tubes. 
These fluids, exposed freely to the optically pure air within 
this chamber, then remained indefinitely free from micro- 
organisms, thus demonstrating that putrescible fluids may 
be freely exposed to air from which the floating particles 
have been removed, and not show a trace either of spoiling 
or of organic life within them. 
It might be objected that the continued boiling of the 
fluids had produced chemical changes inimical to life, or in 
some way destroyed their life-supporting properties; but 
after they had remained for months in a perfectly clear state, 
Tyndall opened the little door in the back of the box and 
closed it at once, thereby admitting some of the floating 
particles from the outside air. Within a few days’ time the 
fluids which previously had remained uncontaminated were 
spoiling and teeming with living organisms. 
These experiments showed that under the conditions of 
the experiments no spontaneous origin of life takes place. 
But while we must regard the hypothesis of spontaneous 
generation as thus having been disproved on an experimental 
basis, it is still adhered to from the theoretical standpoint 
by many naturalists; and there are also many who think 
that life arises spontaneously at the present time in ultra- 
microscopic particles. Weismann’s hypothetical ‘‘biophors,” 
too minute for microscopic observation, are supposed to arise 
by spontaneous generation. This phase of the question, 
