oxidation
fermentations is afforded by the recent discovery that not only bacteria
and fungi, but even the living cells of higher plants, contain peculiar
enzymes which possess the remarkable property of "carrying" oxygen--much as
it is carried in the sulphuric acid chamber--and which have therefore been
termed oxydases. It is apparently the presence of these oxydases which
causes certain wines to change colour and alter in taste when poured from
bottle to glass, and so exposed to air.

[Illustration: FIG. 19.--Ginger-beer plant, showing yeast (_Saccharomyces
pyriformis_) entangled in the meshes of the bacterium (_B. vermiforme_).
(H. M. W.)]

[Sidenote: Bacteria and light.]

Much as the decade from 1880 to 1890 abounded with investigations on the
reactions of bacteria to heat, so the following decade was remarkable for
discoveries regarding the effects of other forms of radiant energy. The
observations of Downes and Blunt in 1877 left it uncertain whether the
bactericidal effects in broth cultures exposed to solar rays were due to
thermal action or not. Further investigations, in which Arloing, Buchner,
Chmelewski, and others took part, have led to the proof that rays of light
alone are quite capable of killing these organisms. The principal questions
were satisfactorily settled by Marshall Ward's experiments in 1892-1893,
when he showed that even the spores of _B. anthracis_, which withstand
temperatures of 100deg C. and upwards, can be killed by exposure to rays of
reflected light at temperatures far below anything injurious, or even
favourable to growth. He also showed that the bactericidal action takes
place in the absence of food materials, thus proving that it is not merely
a poisoning effect of the altered medium. The principal experiments also
indicate that it is the rays of highest refrangibility--the blue-violet and
ultra-violet rays of the spectrum--which bring about the destruction of the
organisms (figs. 17, 18). The practical effect of the bactericidal action
of solar light is the destruction of enormous quantities of germs in
rivers, the atmosphere and other exposed situations, and experiments have
shown that it is especially the pathogenic bacteria--anthrax, typhoid,
&c.--which thus succumb to light-action; the discovery that the electric
arc is very rich in bactericidal rays led to the hope that it could be used
for disinfecting purposes in hospitals, but mechanical difficulties
intervene. The recen