From all this it is evident that the singer or speaker must guard against everything unfavorable, to an extent that an ordinary person need not. The stomach, as the diagram is also meant to show, may express itself on the brain, and give rise, as in fact it often does, owing to indiscretion in eating, to unpleasant outward effects on the muscles required in singing or speaking. Of course, no attempt has been made in the above figure to express anatomical forms and relations exactly.] When all the ingoing impulses from the lungs, etc., are cut off, if respiration does not actually cease, it is carried out in a way so ineffective that life cannot be long sustained. It follows that as the muscular contractions necessary for the chest and other respiratory movements are dependent on the impulses passing in from the lungs, etc., breathing belongs to the class of movements known as reflex--chiefly so, at all events. It will thus be seen that respiration is a sort of self-regulative process, the movements being in proportion to the needs of the body. The greater the need for oxygen, the more are the nerve-terminals in the lungs and the centre itself stimulated, with, as a result, corresponding outgoing impulses to muscles. As the respiratory centre is readily reached by impulses from every part of the body, like one who keeps open house, there are many different sorts of visitors, not all desirable. If, for example, a drop of a fluid that produces no special effect when on the tongue gets into the larynx, trachea, or lungs, the most violent coughing follows. This is one illustration of the _protective_ character of many reflexes. This violent action of the respiratory apparatus is not in itself a desirable thing, because it disturbs if it does not exhaust, but it is preferable to the inflammation that might result if the fluid, a bread-crumb, etc., were to pass into the lungs. In like manner, the deep breath and the "Oh!" that follow a fear-inspiring sight, a very loud noise, or a severe pinch of the skin, are examples of reflex action. They are quite independent of the will, though in some cases they may be prevented by it.