ATMOSPHERE IN RELATION TO PUTREFACTION AND INFECTION. 
43 
characteristic smells. In no instance is the least countenance lent to the notion that an 
infusion deprived by heat of its inherent life, and placed in contact with air cleansed of 
its visibly suspended matter, has any power whatever to generate life anew. 
If it should be asked how I have assured myself that the protected liquids do not 
contain Bacteria , I would, in the first place, reply that with the most careful micro- 
scopic search I have been unable to find them. But much more than this may be 
affirmed. The electric or the solar beam is a far more powerful and searching test in 
this matter than the microscope. In the foregoing pages I have more than once 
described the clearness of my protected infusions, after months of exposure, as equal to 
that of distilled water. So far is this from being an exaggeration, that it falls short of the 
truth ; for I have never seen distilled water so free from suspended particles as the pro- 
tected infusions prove themselves to be. When for months a transparent liquid thus 
defies the scrutiny of the searching beam, maintaining itself free from every speck which 
could scatter light as a Bacterium scatters it — when, moreover, an adjacent infusion, 
prepared in precisely the same way, but exposed to the ordinary air, becomes first hazy, 
then turbid, and ends by wholly shattering the concentrated beam into irregularly 
scattered light, I think we are entitled to conclude that Bacteria are as certainly absent 
from the one as they are present in the other. (See Note I. at the end.) 
For the right interpretation of scientific evidence something more than mere sharpness 
of observation is requisite, very keen sight being perfectly compatible with very weak 
insight. I was therefore careful to have my infusions inspected by biologists, not only 
trained in the niceties of the microscope, but versed in all the processes of scientific 
reasoning. Their conclusion is that it would simply weaken the demonstrative force of 
the experiments to appeal to the microscope at all. 
§ 16. Suspended Particles in Air and Water ; their relation to Bacteria. 
Examined by the concentrated solar rays, or by the condensed electric beam, the 
floating matter of the air is seen to consist: — first, of particles so coarse that their 
individual motions can be followed by the eye ; secondly, of a finer matter which is not 
to be distinguished as motes, but which emits a uniform and changeless light. In this 
finer matter the coarser motes move as in a medium. 
As regards the production of colour, the action of small particles has been examined 
by Brucke in a paper “On the Colours of Turbid Media”*. In relation to the 
question of polarization, Professor Stokes has made some remarks in his memoir 
“ On the Change of the Refrangibility of Light ”f. I may also be permitted to refer 
to my own papers “ On New Chemical Reactions by Light ” and “ On the Blue Colour 
of the Sky,” in the Proceedings of the Royal Society for 1868-69, and to a paper 
“ On the Action of Rays of High Refrangibility on Gaseous Matter,” in the Philosophical 
Transactions for 1870. M. Soret, Lord Rayleigh, and Mr. Bosanquet have also worked 
at this subject, which, as far as it now concerns us, a few words wili render clear. 
* Fogg. Ann. lxxxviii. p. 363. t Philosophical Transactions, vol. 142, pp. 529-530 
MDCCCLXXVI. H 
