with problems of immense interest in pure chemistry, and in animal and
vegetable morphology. Its physiology is not less rich in subjects for
inquiry. Take, for example, the singular fact that yeast will increase
indefinitely when grown in the dark, in water containing only tartrate
of ammonia, a small percentage of mineral salts, and sugar. Out of
these materials the _Torulae_ will manufacture nitrogenous protoplasm,
cellulose, and fatty matters, in any quantity, although they are
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 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.