ed of light, live.

If any of them possess the same powers as yeast (and the same capacity
for living without light is exhibited by some other fungi) there would
seem to be no difficulty about the matter.

Of the pathological bearings of the study of yeast, and other such
organisms, I have spoken elsewhere. It is certain that, in
some animals, devastating epidemics are caused by fungi of low
order--similar to those of which _Torula_ is a sort of offshoot. It is
certain that such diseases are propagated by contagion and infection,
in just the same way as ordinary contagious and infectious diseases
are propagated. Of course, it does not follow from this, that all
contagious and infectious diseases are caused by organisms of as
definite and independent a character as the _Torula_; but, I think,
it does follow that it is prudent and wise to satisfy oneself in each
particular case, that the "germ theory" cannot and will not explain
the facts, before having recourse to hypotheses which have no equal
support from analogy.

V.

ON THE FORMATION OF COAL.

The lumps of coal in a coal-scuttle very often have a roughly cubical
form. If one of them be picked out and examined with a little care, it
will be found that its six sides are not exactly alike. Two opposite
sides are comparatively smooth and shining, while the other four are
much rougher, and are marked by lines which run parallel with the
smooth sides. The coal readily splits along these lines, and the split
surfaces thus formed are parallel with the smooth faces. In other
words, there is a sort of rough and incomplete stratification in the
lump of coal, as if it were a book, the leaves of which had stuck
together very closely.

Sometimes the faces along which the coal splits are not smooth, but
exhibit a thin layer of dull, charred-looking substance, which is
known as "mineral charcoal."

Occasionally one of the faces of a lump of coal will present
impressions, which are obviously those of the stem, or leaves, of a
plant; but though hard mineral masses of pyrites, and even fine mud,
may occur here and there, neither sand nor pebbles are met with.

When the coal burns, the chief ultimate products of its combustion
are carbonic acid, water, and ammoniacal products, which escape up the
chimney; and a greater or less amount of residual earthy salts, which
take the form of ash. These products are, to a great extent, such as
would result from the burning of so