A second kind of control of the smooth muscles and glands is their control through the emotions. We have already given illustrations of this in the paling of the skin when one is frightened, or the erection of the hairs in the tail of an angry cat. For a long time it has been known that most of our emotions, if not all of them, are accompanied by some sort of bodily change; laughter and crying are familiar illustrations. To a certain extent, as in these instances, skeletal muscles share in the bodily effects of emotions, but their most important examples are found in the smooth muscles and glands. Every serious display of emotion is accompanied by a discharge of nervous disturbances into some of the smooth muscles or some of the glands. This fact has long been known, but its meaning has become clear only very recently. Before attempting to explain this, an additional word will be necessary about the nervous control of smooth muscles. These muscles differ from skeletal muscles in one important particular, which is this: when a skeletal muscle is aroused to contraction, it will relax as soon as the stream of nervous disturbances stops. To keep it in contraction a continuous stream must come into it through the nervous system. This is not true of smooth muscle. When a smooth muscle has been caused to contract, it is very likely to stay contracted without further action on the part of the nervous system. In fact, in very many cases another kind of nervous disturbance must be sent into it in order to make it relax. This means that the smooth muscles, or at least most of them, have two sets of nerves coming to them; one set which causes them to contract, the other set which causes them to relax. Both these sets of nerves are of the type described above as supplying the smooth muscles and glands. A good illustration of the double action is found in the stomach. There is one set of nerves whose activity causes the walls of the stomach to perform the churning motions which go on ordinarily during digestion. There is another set of nerves whose effect upon the stomach is to cause all motions in it to stop. This same double arrangement of nerves is found in many of our most important smooth muscle organs. We said a moment ago that every emotional display is accompanied by an outflow of nervous disturbances to the smooth muscle or gland structures. We now see that what happens in the body is determined by which of the possible pathways is followed by the nervous disturbance. One turns pale, when frightened, because in the emotion of fright the nervous discharge is over the nerves that cause the blood vessels of the face to contract. The mouth waters at the sight of delicious food, because the pleasurable emotions aroused thereby cause the nerves to the salivary glands to become active. As was said a moment ago, for a long time there seemed to be no rhyme or reason about these emotional reactions. Why, for example,