8. With a pair of bone forceps, or nippers, break away the skull until the entire brain can be removed from the cavity. Examine the different divisions, noting the relative position and size of the parts. 9. With a sharp knife cut sections through the different parts, showing the positions of the "gray matter" and of the "white matter." NOTE.—If the entire class is to examine one specimen, it is generally better to have the dissecting done beforehand and the parts separated and tacked to small boards. This will permit of individual examination. Sketches of the sciatic nerve, brachial plexus, and of sections through the brain and spinal cord should be made. *Location of Nerves in the Body.*—Several of the nerves of the body lie sufficiently near the surface to be located by pressure and are easily recognized as sensitive cords. Slight pressure from the fingers reveals the presence of nerves in the grooves of the elbow (the crazy bone), between the muscles on the inner side of the arm near the shoulder, and in the hollow part of the leg back of the knee. These are all large nerves. Small nerves may be located in the same manner in the face and neck. CHAPTER XVIII - PHYSIOLOGY OF THE NERVOUS SYSTEM In the preceding chapter was pointed out the method by which the different parts of the body are brought into communication by the neurons or nerve cells. We are now to study the means whereby the neurons are made to control and coördinate the different parts of the body and bring about the necessary adjustment of the body to its surroundings. This work of the neurons naturally has some relation to their properties. *Properties of Neurons.*—The work of the neurons seems to depend mainly upon two properties—the property of irritability and the property of conductivity. _Irritability_ was explained, in the study of the muscles (page 243), as the ability to respond to a stimulus. It has the same meaning here. The neurons, however, respond more readily to stimuli than do the muscles and are therefore more irritable. Moreover, they are stimulated by all the forces that induce muscular contraction and by many others besides. They are by far the most irritable portions of the body. _Conductivity_ is the property which enables the effect of a stimulus to be transferred from one part of a neuron to another. On account of this property, an excitation, or disturbance, in any part of a neuron is conducted or carried to all the other parts. Thus a disturbance at the distant ends of the dendrites causes a movement toward the cell-body and, reaching the cell-body, the disturbance is passed through it into the axon. This movement through the neuron is called the _nervous impulse_.