e wholly
deprived of those rays of the sun, the influence of which is essential to
the growth of ordinary plants. There has been a great deal of speculation
lately, as to how the living organisms buried beneath two or three
thousand fathoms of water, and therefore in all probability almost
deprived 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 one's self 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

[1870]

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 c