ose, the cotton, hay, &c., having
been converted into a highly porous friable and combustible mass, may then
ignite in certain circumstances by the occlusion of oxygen, just as
ignition is induced by finely divided metals. A remarkable point in this
connexion has always been the necessary conclusion that the living bacteria
concerned must be exposed to temperatures of at least 70deg C. in the hot
heaps. Apart from the resolution of doubts as to the power of spores to
withstand such temperatures for long periods, the discoveries of Miquel,
Globig and others have shown that there are numerous bacteria which will
grow and divide at such temperatures, _e.g._ _B. thermophilus_, from
sewage, which is quite active at 70deg C., and _B. Ludwigi_ and _B.
ilidzensis_, &c., from hot springs, &c.

[Sidenote: Phosphorescent bacteria.]

The bodies of sea fish, _e.g._ mackerel and other animals, have long been
known to exhibit phosphorescence. This phenomenon is due to the activity of
a whole series of marine bacteria of various genera, the examination and
cultivation of which have been successfully carried out by Cohn, Beyerinck,
Fischer and others. The cause of the phosphorescence is still a mystery.
The suggestion that it is due to the oxidation of a body excreted by the
bacteria seems answered by the failure to filter off or extract any such
body. Beyerinck's view that it occurs at the moment peptones are worked up
into the protoplasm cannot be regarded as proved, and the same must be said
of the suggestion that the phosphorescence is due to the oxidation of
phosphoretted hydrogen. The conditions of phosphorescence are, the presence
of free oxygen, and, generally, a relatively low temperature, together with
a medium containing sodium chloride, and peptones, but little or no
carbohydrates. Considerable differences occur in these latter respects,
however, and interesting results were obtained by Beyerinck with mixtures
of species possessing different powers of enzyme action as regards
carbohydrates. Thus, a form termed _Photobacterium phosphorescens_ by
Beyerinck will absorb maltose, and will become luminous if that sugar is
present, whereas _P. Pflugeri_ is indifferent to maltose. If then we
prepare densely inseminated plates of these two bacteria in gelatine
food-medium to which starch is added as the only carbohydrate, the bacteria
grow but do not phosphoresce. If we now streak these plates with an
organism, _e.g._ a yeast, which