e for ten or twelve hours, and the process of heating is
repeated. We thus kill the germs in order of their resistance, and
finally kill the last of them. No infusion can withstand this process
if it be repeated a sufficient number of times. Artichoke, cucumber,
and turnip infusions, which had proved specially obstinate when
infected with the germs of desiccated hay, were completely broken down
by this method of discontinuous heating, three minutes being found
sufficient to accomplish what three hundred minutes' continuous
boiling failed to accomplish. I applied the method, moreover, to
infusions of various kinds of hay, including those most tenacious of
life. Not one of them bore the ordeal. These results were clearly
foreseen before they were realised, so that the germ theory fulfils
the test of every true theory, that test being the power of prevision.

When 'naked or almost naked specks of protoplasm' are spoken of, the
imagination is drawn upon, not the objective truth of Nature. Such
words sound like the words of knowledge where knowledge is really nil.
The possibility of a 'thin covering' is conceded by those who speak in
this way. Such a covering may, however, exercise a powerful
protective influence. A thin pellicle of India-rubber, for example,
surrounding a pea keeps it hard in boiling water for a time sufficient
to reduce an uncovered pea to a pulp. The pellicle prevents
imbibition, diffusion, and the consequent disintegration. A greasy or
oily surface, or even the layer of air which clings to certain bodies,
would act to some extent in a similar way. 'The singular resistance
of green vegetables to sterilisation,' says Dr. William Roberts,
'appears to be due to some peculiarity of the surface, perhaps their
smooth glistening epidermis which prevented complete wetting of their
surfaces.' I pointed out in 1876 that the process by which an
atmospheric germ is wetted would be an interesting subject of
investigation. A dry microscope covering-glass may be caused to float
on water for a year. A sewing-needle may be similarly kept floating,
though its specific gravity is nearly eight times that of water.

Were it not for some specific relation between the matter of the germ
and that of the liquid into which it falls, wetting would be simply
impossible. Antecedent, to all development there must be an
interchange of matter between the germ and its environment; and this
interchange must obviously depen