performing all of these functions. But in the higher forms each organ not only
has its own specific work, but even within the same organ each part has its own
particular function assigned. Thus we have seen that the two parts of the neurone
probably perform different functions, the cells generating energy and the fibers
transmitting it.
It will not seem strange, then, that there is also a division of labor in the cellular
matter itself in the nervous system. For example, the little masses of ganglia
which are distributed at intervals along the nerves are probably for the purpose
of reënforcing the nerve current, much as the battery cells in the local telegraph
office reënforce the current from the central office. The cellular matter in the
spinal cord and lower parts of the brain has a very important work to perform in
receiving messages from the senses and responding to them in directing the
simpler reflex acts and movements which we learn to execute without our
consciousness being called upon, thus leaving the mind free from these petty
things to busy itself in higher ways. The cellular matter of the cortex performs
the highest functions of all, for through its activity we have consciousness.
FIG. 13.—Side view of left hemisphere of human brain, showing the principal localized areas.The gray matter of the cerebellum, the medulla, and the cord may receive
impressions from the senses and respond to them with movements, but their
response is in all cases wholly automatic and unconscious. A person whose
hemispheres had been injured in such a way as to interfere with the activity of
the cortex might still continue to perform most if not all of the habitual
movements of his life, but they would be mechanical and not intelligent. He
would lack all higher consciousness. It is through the activity of this thin
covering of cellular matter of the cerebrum, the cortex, that our minds operate;