Experiment 129. Obtain a sheep’s kidney in good order. Observe that its shape is something like that of a bean, and note that the concave part (hilus), when in its normal position, is turned towards the 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 coördination 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, as in sight, smell, taste, or hearing,—every instinct, every act of the will, and every thought are possible only through the action of the nerve centers.