=Respiratory Centres, Inspiratory and Expiratory= are in the floor of the fourth ventricle between the centres for the vagus and accessory nerves, and are directly stimulated by the CO_{2} in the blood. Secondary subsidiary centres are in the optic thalamus, in the corpora quadrigemini both anterior and posterior pairs, and finally in the cervical spinal cord, so that disorder of respiration may occur from lesions in these points as well as in the main oblongata centre. =Respiratory Inhibition= and arrest depend on the vagus, the superior and inferior laryngeal nerves. =The Salivation Centre= also lies in the floor of the fourth ventricle and stimulation of the medulla causes free secretion. =The Centres for Sneezing, Coughing, Sucking, Chewing, Swallowing and Vomiting= are also seated in the oblongata, so that any one of these phenomena may come from a central irritation. In _bulbar paralysis_ the loss of power usually extends from the tongue through the lips, cheeks, jaws, pharynx, larynx, to the respiratory muscles and heart. Coughing may be roused by irritation of the external auditory meatus, liver, stomach, bowels, or generative organs as well as from the air passages. =Cardiac Accelerating and Inhibiting Centres= are both present in the bulb, the latter receiving its afferent impulse mainly through the vagus nerve. Stimulation of the vagi, anæmia of the bulb through decapitation or through tying both carotids, hyperæmia through tying of the jugulars, a venous state of the blood, and blows on the abdomen all slow or arrest the heart action. Digitalis or muscarin has a similar effect. The heart action is accelerated by febrile and inflammatory affections, by a high or low temperature by section of the vagi, by sipping of cold water, by atropine or curari, and by salts of soda. Potash salts on the other hand restore the inhibitory action of the vagi and lower the heart’s action. =The Vaso-Motor Center= is also in the oblongata and the contraction of the vessels with increase of arterial pressure may ensue from afferent currents in the sympathetic nerve and many sensory trunks. The varying activity is seen in blushing, in the congestion of mucous membranes under rage or excitement, in the capillary contraction in the early stage of inflammation, in the second stage of capillary dilation, in angioma or nævus and in extensive congestions and hæmorrhages in different organs. The arrest of bleeding under fainting is due largely to the anæmia of this centre.