A good illustration of the full-blooded type of headache is that which so very frequently, indeed almost invariably, occurs in the early stage of a fever or other acute infection, such as typhoid, pneumonia, or blood-poisoning, Here the face is red, the eyes are bloodshot and abnormally bright, the pulse is rapid and full, the headache so severe as to become the first disabling symptom in the disease,—all because this is the effect of the poison (toxin) of the disease upon the heart, the temperature, and the surface blood-vessels. Fortunately for the sufferer, this head-pain, like most others in the course of severe infections, is only preliminary, for as soon as the tissues of the body have become thoroughly saturated with the toxins, the nerves become dulled and semi-narcotized, so that they no longer respond with the pain-cry. As the patient settles down into the depression and dullness of the regular course of the fever, the headache usually subsides into little more than a sense of heaviness, or oppression and vague discomfort.
Moral: It is a sign of health to be able to feel a headache, an indication that your body is still fighting vigorously against the enemy, whether traitor within or foe without.
On the other hand, many of our most agonizing, and particularly our most persistent and obstinate headaches, occur in individuals who are markedly anæmic, with a low, weak pulse, poor circulation, blanched lips, and dull, lackluster eyes. The one and only thing in common between these two classes of "head-achers" is that their blood and tissues are loaded with poisons. Whether produced by invading germs or by starvation and malnutrition of the body-tissues makes no difference to the headache nerves. Their business, like good watchdogs, is to bark every time they smell danger of any sort, whether it be bears or book-agents. One of the most valuable services rendered us by our priceless heads is aching.
This view of the nature of headache explains at once why it is so extraordinarily frequent and so extraordinarily varied in causation. It is not too much to say that any influence that injuriously affects the body may cause a headache. It would, of course, be idle even to attempt to enumerate the different causes and kinds of this pain, as it would involve a review of the entire environment of the human species, internal and external. It makes not the slightest difference how the poison gets into the blood, or where it starts. A piece of tainted meat or a salad made from spoiled tomatoes will produce a headache just as promptly and effectively as an over-exposure to the July sun or an attack of influenza. It is even practically impossible to pick out from such a wealth of origins two or three, or even a score of, conditions which are the most frequent, most important, or the most interesting causes. The most exasperating thing about dealing with a headache is that we never know, until its history has been most carefully examined, whether we have to do with a mere temporary expression of discomfort and unbalance, due to overfatigue, errors in diet, a stuffy room, lack of exercise, or what-not, which can be promptly relieved by removing the cause; or whether we have to deal with the first symptoms of a dangerous fever, the beginning of a nervous breakdown, or an early warning of some grave trouble in kidneys, liver, or heart.
The one thing, however, that stands out clearly is that headache always means something; that it should be promptly and thoroughly investigated with a view to finding and removing the cause,—never as something which is to be cured as quickly as possible, as the police cure social discontent, by clubbing it over the head, with some narcotic or other symptom-smotherer. Nor should it be regarded as a malady so trifling that it is best treated with contempt, and still less as a mere "thorn in the flesh," whose ignoring is to be counted a virtue, or whose patient endurance without sign a mark of saintship. Martyrdom is magnificent when it is necessary, but many forms of it are sheer stupidity. Don't either gulp down some capsule, or "grin and bear it." Look for the cause. The more trivial it is, the easier it will be to discover and remove before serious harm has been done. The less easy you find it to put your finger upon it, the more likely it is to be serious or chronic, and the more necessary it is to remove it.
Once, however, we have clearly recognized that no headache should be treated too lightly or indifferently, it may be frankly admitted that practically the vast majority of headaches in which we are keenly interested—that is, the kind that we individually or the members of our family habitually indulge in—do form a moderately uniform class among the hundreds of varieties, and are in the main due to some six or seven great groups of causes. We have learned by repeated and unpleasant experience that they are very apt to "come on" in about a certain way, after a certain set of circumstances; that they last about so long, that they are made worse by such and such things, that they are helped by other things, and that they generally get better after a good night's sleep.
One of the commonest causes of this group of recurrent and self-limited headaches is fatigue, whether bodily, mental, or emotional. This was long an apparent stumbling-block in the way of a poison theory of headache, but now it is one of its best illustrations. Physiologists years ago discovered that what produced not merely the sensation but also the fact of fatigue, or tiredness, was the accumulation in the muscles or nerves of the waste-products of their own activities. Simply washing these out with a salt solution would start the utterly fatigued muscle contracting again, without any fresh nourishment or even period for rest. It has become an axiom with physiologists that fatigue is simply a form of self-poisoning, or, as they sonorously phrase it, autointoxication. One of the reasons why we are so easily fatigued when we are already ill, or, as we say, "out of sorts," is that our tissues are already so saturated with waste-products or other poisons that the slightest addition of the fatigue poisons is enough to overwhelm them. This also explains why our pet variety of headache, which we may have clearly recognized to be due to overwork or overstrain of some sort, whether with eye, brain, or muscles, is so much more easily brought on by such comparatively small amounts of over-exertion whenever we are already below par and out of sorts. People who are "born tired," who are neurasthenic and easily fatigued and "ached," are probably in a chronic state of self-poisoning due to some defect in their body-chemistry. Further, the somewhat greater frequency and acuteness of headache in brain workers—although the difference between them and muscle workers in this regard has been exaggerated—is probably due in part to the greater sensitiveness of their nerves; but more so to the curious fact, discovered in careful experiments upon the nervous system, that the fatigue products of the nerve-cells are the deadliest and most powerful poisons produced in the body. Hence some brain workers can work only a few half-hours a day, or even minutes at a time; for instance, Darwin, Spencer, and Descartes.
A very frequent cause of these habitual headaches, really a subdivision of the great fatigue group, is eye-strain. This is due to an abnormal or imperfect shape of the eye, which is usually present from birth. Hence, the only possible way of correcting it is by the addition to the imperfect eye of carefully fitted lenses or spectacles which will neutralize this mechanical defect. To put it very roughly, if the eye is too flat to bring the light-rays to a focus upon the retina, which is far the commonest condition (the well-known "long sight," or hyperopia), we put a plus or bulging glass before the eye and thus correct its shape. But if the eye is too round and bulging, producing the familiar "short sight," or myopia, we put a minus or concave lens before the eye, and thus bring it back to the normal. By a curious paradox, however, it often happens that the headache due to eye-strain is caused not by the grosser defects, such as interfere with vision so seriously as absolutely to demand the wearing of glasses to see decently, but from slighter and more irregular degrees and kinds of misshapenness in the eye, most of which fall under the well-known heading of astigmatism. These interfere only slightly with vision, but keep the eye perpetually on the strain, on a twist, as it were, rasping the entire nervous system into a state of chronic irritation. Our motto now, in all cases of chronic headache, is, first examine the patient's habits of life, next his eyes.
Many forms of headache are really stomach-ache in disguise, due to digestive disturbances, the absorption of poisons from the food-tube, whether from tainted, spoiled, or decayed foods, as in the now familiar ptomaine poisoning, or from imperfect processes of digestion. The immediate effect, however, of diet in the causation of headache is not so great as we once believed. We have no adequate basis for believing that any particular kinds or amounts of food are especially likely to produce either headache or what we might call the headache habit, except in so far as they upset the digestion. In a certain number of susceptible individuals, however, it will be found that some particular kind of food, often perfectly wholesome and harmless in itself, will bring on an attack of headache whenever it is indulged in. Very frequently the disturbances of digestion which are put down as the cause of a headache are only symptoms of some general constitutional lack of balance, as eye-strain or neurasthenia, which is the cause of both these discomforts. Far fewer headaches can be cured by dieting than we at one time believed, and underfeeding is a more frequent cause than overeating.
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.