rom getting too
hot, muscles in the arteries going to the skin relax, thereby allowing
more blood to flow to the surface, where the heat can be disposed of
through radiation and through the evaporation of the perspiration. On the
other hand, if the body is in danger of losing too much heat, the muscles
in the walls of arteries going to the skin are made to contract and those
to internal organs relax, so that less blood flows to the skin and more to
the internal organs. In this way the nervous system adjusts the
circulation to suit the conditions of temperature outside of and within
the body and, in so doing, maintains the normal body temperature.

*Summary.*--The nervous system is able to control, cooerdinate, and adjust
the different organs of the body through its intimate connection with all
parts and through a stimulus (the nervous impulse) which it supplies and
transmits. Nervous impulses, excited by external stimuli, follow definite
paths and cause activity in the different parts of the body. All such
pathways are through the central nervous system. In reflex action the
impulses are mainly through the spinal cord, but to some extent through
the bulb, pons, and midbrain. In voluntary action they pass through the
cerebrum--a condition that leads to important modifications in the results.
The cerebrum, in addition to controlling the voluntary movements, is able
to establish the necessary conditions for secondary reflex actions, such
as walking, writing, etc. Although certain of the divisions of the nervous
system exercise special functions, all parts of it are closely related.

Exercises.--1. Give the function of each of the parts of a neuron.

2. State the purpose of the nervous impulse.

3. Show that the exciting cause of bodily action is outside of the nervous
system and, to a large extent, outside of the body.

4. Describe the arrangement that enables stimuli outside of the body to
cause action within the body.

5. Describe a reflex action and show how it is brought about.

6. Distinguish between afferent, efferent, and intermediate neurons.

7. Draw diagrams showing the impulse pathways in voluntary and in reflex
action.

8. What purposes are served by the sympathetic neurons?

9. Describe the method of control of the circulatory and digestive
processes. How do reflex actions protect the body?

10. Compare voluntary and reflex action. In what sense are all the
activities of the body reflex?

11. In w