. Physiology, experimental and descriptive . hence animpulse is taken by the pneumogastricnerves to stop the heart. In the experiment with the rabbitsear we saw that stimulating the sympa-thetic nerve caused the ear to becomepale. This, we understand, is due tothe constriction of the arte-ries of the ear, because thenerves have made the musclefibers of these arteries short-en. Such nerve fibers arecalled Constrictors, or Vaso-constrictors. They run inthe sympathetic nerve, buthave their origin and centerin the spinal bulb. Otherfibers may cause the opposite effect,namely, dilation, and are the
. Physiology, experimental and descriptive . hence animpulse is taken by the pneumogastricnerves to stop the heart. In the experiment with the rabbitsear we saw that stimulating the sympa-thetic nerve caused the ear to becomepale. This, we understand, is due tothe constriction of the arte-ries of the ear, because thenerves have made the musclefibers of these arteries short-en. Such nerve fibers arecalled Constrictors, or Vaso-constrictors. They run inthe sympathetic nerve, buthave their origin and centerin the spinal bulb. Otherfibers may cause the opposite effect,namely, dilation, and are thereforecalled Vaso-dilators. Examples ofthese may be found running to thearteries of the limbs. We have seenthat when the muscles of any organ, say the legs, act, they need a greater supply of blood. Now,at the same time that nerve impulses are sent to the musclesof the legs to make the muscles shorten, impulses are sentalong other fibers of the same nerves to make the arteriesdilate, and allow more blood to flow to, these muscles. Stomach ~. Flg. 35. Diagrair jf Pneu*mogastric Nerve. EFFECTS OF ALCOHOL. 93 The vaso-constrictor nerves and the vaso-dilator nervestaken together are called Vaso-motor nerves. There is no evidence that the sympathetic ganglia arecenters of reflex action. Let us be alert to discover the action of these nerves as westudy other parts of the body. EFFECTS OF ALCOHOL ON THE CIKCTJLATION. Alcohol stimulates the heart, producing increased forceand rapidity of the cardiac beat. It thus tends to increase theblood-pressure by acting on the heart, and. to increase the flowof blood from the arteries into the veins. The effect on theblood-pressure is, however, partly counteracted by a coincidentdilatation of the blood-vessels of the skin, which thus becomeflushed, and tends to produce more sensible perspiration. —Treatise on Hygiene, Stevenson and Murphy. The warm and flushed condition of the skin which fol-lows the drinking of alcoholic fluids is probably, in
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