m of the single cell. There is a circulatory system, a
respiratory system, etc.; but we must once more point out that such
systems are made up of cells, so that every function of the highest
animal may be finally reduced to what takes place in the unicellular
animal. A circulatory system consists of a heart and blood-vessels,
all filled with blood, which latter is "the life," as was known from
the earliest times; yet this same blood is of no more use for the
nourishment of the body while it is contained in those tubes which
constitute the blood-vessels than is bread locked up in a pantry to a
hungry boy. That which really provides the nutriment for the body is a
fluid derived from the blood, a something like the liquid part of
blood and known as _lymph_. This latter is to the cells of any tissue,
as a muscle, as is the water filled with the food on which an amoeba
lives. In like manner, in spite of the complicated apparatus which
supplies oxygen and removes carbon dioxide, the respiratory system,
respiration is finally the work of the cell, as in amoeba; a
muscle-cell respires exactly as does the one-celled animal.

When we consider the marvellous complexity of structure of one of the
higher animals, and the amazing variety of its functions, the question
naturally arises as to how all this is brought about without any sort
of clashing of the interests of one part with those of another. Why is
it that the stomach has enough and not too much blood? By what means
has Nature solved the problem of supplying more oxygen to parts in
action than to those at rest? How is it that one set of muscles acts
with instead of antagonizing another set, as in any complicated series
of movements, such as walking?

To bring about this harmonization, or _co-ordination_, the nervous
system has been provided. As the nervous and muscular systems are of
preeminent importance in voice-production, they will now be considered
with more detail than it is necessary to give to other systems.

Complicated as is the nervous system, modern advances in the sciences
of anatomy and physiology have made the comprehension of the subject
easier. It is now known that the nervous system, in spite of its wide
ramifications, is also made up of cells which are structurally and
functionally related to each other, and make connection with every
part of the whole community, the body. A nerve-cell, or _neurone_, may
be very complicated in its structure because of its