backbone. Notice that all the vessels leave and enter the kidney at the
hilus. Observe a small thick-walled vessel with open mouth from which
may be pressed a few drops of blood. This is the renal artery. Pass a
bristle down it. With the forceps, or even with a penknife, lift from
the kidney the fine membrane enclosing it. This is the kidney capsule.

Divide the kidney in halves by a section from its outer to near its
inner border. Do not cut directly through the hilus. Note on the cut
surfaces, on the outer side, the darker cortical portion, and on the
inner side, the smooth, pale, medullary portion. Note also the pyramids
of Malpighi.

Chapter X.

The Nervous System.

260. General View of the Nervous System. Thus far we have learned
something of the various organs and the manner in which they do their
work. Regarding our bodily structure as a kind of living machine, we have
studied its various parts, and found that each is designed to perform some
special work essential to the well-being of the whole. As yet we have
learned of no means by which these organs are enabled to adjust their
activities to the needs of other tissues and other organs. We are now
prepared to study a higher, a more wonderful and complex agency,--the
nervous system, the master tissue, which controls, regulates, and
directs every other tissue of the human body.

The nervous system, in its properties and mode of action, is distinct from
all the other systems and organs, and it shares with no other organ or
tissue the power to do its special work. It is the medium through which
all impressions are received. It connects all the parts of the body into
an organism in which each acts in harmony with every other part for the
good of the whole. It animates and governs all movements, voluntary or
involuntary,--secretion, excretion, nutrition; in fact all the processes
of organic life are subject to its regulating power. The different organs
of the body are united by a common sympathy which regulates their action:
this harmonious result is secured by means of the nervous system.

This system, in certain of its parts, receives impressions, and generates
a force peculiar to itself. We shall learn that there can be no physical
communication between or cooerdination of the various parts of organs, or
harmonious acts for a desire result, without the nerves. General
impressions, as in ordinary sensation, or special impressions, a