By an odd _bouleversement_ the one type of headache which we have almost unanimously in the past attributed to digestive disturbances, the famous, or, rather, infamous, "sick headache," is now known to have little or nothing to do with the stomach in its origin. In fact, incredible as it may seem at first sight, it is the headache that causes the sickness, not the sickness the headache. Stop the pain of a sick headache in the early stage, and the sickness will never develop at all. The vomiting of sick headache is an interesting illustration of vomiting due to disturbances of the brain and nervous system, technically known as central vomiting. Another illustration is the vomiting of seasickness, due solely to dizziness from the gross contradiction between the testimony of our eyes and of the balancing canals in the inner ear. The stomach or its contents has no more to do with seasickness than the water in a pump has with the plunger. Injuries to the head will bring on severe and uncontrollable vomiting, and the severer type of fevers is very frequently ushered in by this curious sign. As to what it means, we are as yet utterly in the dark, for in none of these conditions does the process do the slightest good, but simply adds to the discomfort of the situation. It would appear to be a curious echo of ancestral times, when the animal was pretty much all stomach, and hence emptying that organ would probably relieve two-thirds of his discomforts. Whatever the explanation, the fact remains that whenever our nervous system gets about so panic-stricken, it promptly begins throwing its cargo overboard, in the blind hope that this may somehow relieve the situation. The bile that we bring up at the end of these interesting acrobatic performances and which makes us feel so much better,--because we have now got the cause of the trouble out of our system,--is simply due to the prolonged vomiting, which has reversed the normal current and caused the perfectly healthy bile from our unoffending liver to pass upward into the stomach, instead of downward into the bowels. In another great group of headaches natural poisons or waste-products are not burned up or got rid of through the body-sewers and pores as rapidly as they should be; for instance, the familiar headache from sitting too long in a stuffy room. Your well-known and well-earned discomfort is, of course, due in part to the irritating and often poisonous gases, dust, and bacteria, which are present in the air of an unventilated room; but it is also due to the steady piling up of the waste products of your own tissues. These poisons are normally oxidized in the muscles, burned up and exhaled through the lungs, and sweated out through the skin,--all three of which relief agencies are, of course, practically paralyzed, or working at lowest possible level, while you are sitting at your desk.