12 THE THEORY OF THE LIVING ORGANISM

have to the animal as a whole, I believe it follows, if the general
argument to be developed In this book is accepted, that these living
parts of a cell are also subjects, and that therefore the cell is a
subject constituted out of subsidiary subjects. It is, however, not
necessary at present to take up any definite opinion as to the
subject status of the living parts of a cell.4

Living agents may therefore be elementary subjects; for instance,
cells, or if these are considered as nexus of subjects, the sub-agents
of the cell. Or they may be nexus of subjects, whose unity of
action is due to similar environment provided by the biological
field of which they form a part. Or they may be constituted of
a nexus of subjects which in combination give rise to a subject
of higher order. When an agent is constituted in this way, I shall
speak of the subject of higher order as the central agent. The
most conspicuous example of a central agent is the one which
is concerned with the behaviour of the animal as a whole; that is
to say, its behaviour considered as a subject and not merely as
a nexus of subjects. If a cell is to be considered, not only as a
subject but also as a nexus of component subjects, the subject
which is the cell as a whole is the central agent of the cell, having
the same relation to its differentiated living parts as the central
agent of the animal as a whole has to its component subjects.

A central agent might therefore with equal propriety be termed
a central subject. The former term seems preferable however,
for the term 'agent' must be retained to describe a nexus of
subjects, or indeed any nexus of activity, acting as a causal unit
without implying either that it has or has not, as a whole, also
the unity of a subject. To use the term 'central subject' while
retaining the term 'central agent' for the other type of nexus would
suggest that an agent is always to be contrasted with a subject.
Since, however, every living agent, if not itself a subject is at least
a nexus of subjects, it is often less important for the purposes of
our argument to decide whether or not it must be considered
itself a subject than to realize that It is composed of subjects.

Moreover, the word 'agent/ even when that agent is a subject,
is useful as including not only its activity as a subject, but also
its anatomical aspect.

The locus of the Central Agent5 concerned with the behaviour
of the animal as a whole is the brain, especially the cortex in the

4. The relation between 'living' and 'non-living' will receive attention in chapter in,

5. For convenience I shall in future refer to the central agent which is concerned with
the behaviour of the organism as a whole as 'the Central Agent* with capital initial letters.