
~ that atmosphere was charged with bacterial germs in 
such excess as to be proof against subsidence, burn- 
ing, and plugging, and that this excess was due to 
the fact that in one of the rooms of the Institution 
some old hay was to be found. How far this 
deserves consideration as a working hypothesis is a 
question which admits of difference of opinion ; but 
Professor Tyndall would scarcely ask us to accept it 
without proof as the real explanation. Why bacterial 
germs in excess should make their way through a 
sieve ordinarily close enough to exclude them is not 
apparent. Neither is it quite obvious why the red- 
hot platinum, which would burn up all the germs in 
ordinary air, should fail to do so when the con- 
tamination was excessive. And we are not quite 
sure that the subsidence of small particles from 
the air is at all hindered by increasing their 
number ; and if it were, it would not be a very 
serious matter to an observer furnished, as Professor 
Tyndall is, with an optical method of testing the 
purity of the air so delicate as to determine the 
instant when the last particle of germinal or other 
matter has deposited itself. 
‘“Even when these difficulties are got over, there 
is no warrant that we know of for assuming that old 
dry hay will fill the air with swarms of bacterium 
germs. On the contrary, everything at present 
rather points to the hypothesis that desiccation would 
be fatal to bacteria and their germs, if they have 
any.' No doubt it is true, as the professor pointed 
1This is not quite correct. The writer probably had in mind the 
very definite statements made on this subject by Burdon-Sanderson 
P 
