The advantage of the construction of the nerve paths from the spinal cord to the smooth muscles or to the glands is that a single nervous disturbance from the central nervous system can affect many muscle or gland cells all at once. In the case of the skeletal muscles, on the other hand, the only way a great many fibers can be made active at once, is by sending out nervous disturbances through a great many nerve cells. There is undoubted economy in having the control of the smooth muscles and glands carried on by means of comparatively few discharges from the central nervous system. A peculiarity of the structures that we are talking about now is that we have very little voluntary control over them. This contrasts sharply with the completeness of our control over the activities of our skeletal muscles. With very few exceptions we can start, stop, or regulate skeletal muscle activities at pleasure, but the activities of our smooth muscles and of our glands are not under our control in the same way. We cannot cause ourselves to turn pale by an act of the will, nor can we set the stomach to working when we wish. This latter inability is a real misfortune, for there are many cases of acute indigestion that are due to stagnation of the stomach, and if we could set the stomach into operation at will, these would be avoided. Since we have not this voluntary control, it is of the utmost importance for us to learn how the control is really carried on, so that the motions necessary to health can be induced in a normal manner. To a very large extent the smooth muscles and glands are subject to reflex control; that is, nervous disturbances coming in from the sense organs pass over by way of connecting nerve cells to the nerve pathways leading out to the smooth muscles or to the glands. Examples of this kind of control are seen in the paling of the skin, when one is chilly, or its flushing, when one is warm; in the copious secretion of saliva into the mouth that one can get by chewing a rubber band; or in the secretion of tears that comes when the front of the eye is hit.