Vice-President's Address. 15 
which these particles found themselves surrounded, were 
caused to be developed. Only thirty-seven years ago, 
Schroeder and Von Dusch demonstrated an even simpler 
method of depriving the air of its organisms; they found 
that air filtered through a layer of cotton wadding was 
sufficient to render it incapable of producing decomposition 
in infusions from which the germs had already been 
eliminated by heat. Then five or six years later Hoffmann, 
Chevreuil, and Pasteur pointed out that if the narrow neck of 
a bottle in which the germ-free infusion was contained was 
bent downwards, and no strong currents of air were allowed 
to pass from without into the flask, any germ-free fluid 
contained within could undergo no putrefactive changes; and 
they argued that germs, like all other solid particles, are 
amenable to the laws of gravitation, and that when they are 
not carried about by currents they must settle-down upon an 
upper surface, and that for this reason, when the mouth of the 
neck of the bottle was bent downwards, no organisms could 
find their way into the bottle. Tyndall gave demonstrative 
proof of this in his exquisite experiments of smearing the 
inside of a chamber with glass walls with glycerine which 
retained all particles as they fell. After proving their entire 
absence by passing through the chamber a ray of light which 
could only be seen so long as particles remained suspended in 
the atmosphere, he placed vegetable infusions which had been 
sterilised by heat within, with the result that they remained 
free from any trace of any organic life for several weeks 
together. The battle between the adherents of abiogenesis and 
biogenesis was one of the most interesting controversies, and 
one in which more ingenuity was developed than in almost 
any other that had raged for some time. As we know, the 
battle went in favour of those who did not believe in spon- 
taneous generation, and the matter has now been definitely 
set at rest. It is an accepted belief that bacteria, or microbes, 
as these lowly organised forms are now called, may be destroyed 
by heat and by certain chemical reagents, that when once de- 
stroyed in any media no other organisms can rise from their 
ashes, and that such media remain perfectly free from putre- 
factive changes until fresh germs are introduced from without. 
