ironment are adjusted. It consists of a large
central mass, the brain and spinal cord, which is formed in the embryo
by an infolding of the external surface, much in the same way that a
gland is formed; but the connection with the surface is lost in
further development and it becomes completely enclosed. Connected with
the central nervous mass, forming really a part of it and developing
from it, are the nerves, which appear as white fibrous cords and after
dividing and subdividing, are as extremely fine microscopic filaments
distributed to all parts of the body. By means of the nerves all
impressions are conveyed to the brain and spinal cord; all impulses
from this, whether conscious or unconscious, are conveyed to the
muscles and other parts. The brain is the sole organ of psychical
life; by means of its activity the impressions of the external world
conveyed to it through the sense organs are converted into
consciousness. Whatever consciousness is, and on this much has been
written, it proceeds from or is associated with the activity of the
brain cells just as truly as the secretion of gastric juice is due to
the activity of the cells of the stomach. The activity of the nervous
system is essential for extra-uterine life; life ceases by the
cessation of circulation and respiration when either the whole or
certain small areas of its tissue are destroyed. In intra-uterine
life, with the narrow and unchanging environment of the fluid within
the uterine cavity which encloses the foetus, life is compatible with
the absence or rudimentary development of the nervous system. The
foetus in this condition may be otherwise well developed, and it would
be not a misuse of words to say that it was healthy, since it is
adjusted to and in harmony with its narrow environment, but it would
not be normal. The intra-uterine life of the unborn child, it must be
remembered, is carried out by the transmission of energy from the
mother to the foetus by means of the close relation between the
maternal and foetal circulation. It is only when the free existence
demands activities not necessary in intra-uterine life that existence
without a central nervous system becomes impossible.

It is essential in so complicated a structure as the body that some
apparatus should exist to provide for the interchange of material. The
innumerable cell units of the body must have material to provide
energy, and useless material which results from their activity