Poisonous matters are absorbed from the affected surfaces into the blood. These poisons, circulating in the blood, produce great irritation of the nerve cells, so much so, that the severity of the attack is felt in the nervous centres, the brain and spinal cord, with pain varying from the most acute and sharp, to a dull, numb ache. The temples, eyes, neck and small of the back, are in their order, the usual locations of greatest pain. Such attacks vary in frequency and severity. One attack is usually followed by an early recurrence, which may be more or less severe, while the period of active pain varies from a few hours to several days. Such attacks leave an exhausted state of the nerve centres and general weakness of the system that often lasts for weeks and may permanently impair the system, except such results be prevented by appropriate treatment. Every recurrence of the attack leaves the system in a worse condition, until profound nervous prostration; ensues.
Malarial headache, sometimes termed "brow ague," is a common form of the malady with those residing in malarial regions. The pain rapidly develops, usually over one eye. It lasts from five to ten hours, and is often of frightful intensity.
Other forms are rheumatic and gouty headache; usually a heavy aching pain appearing on the approach of storms, but at times almost continuous, made worse by improper diet.
Uræmic headache is due to kidney disease, and alcoholic to direct irritation of the brain membranes from the use of alcoholic beverages. The latter is accompanied with much irritation of the stomach and intestines.
Headaches of a similar character result from the presence in the blood of an excess of the active principles of coffee and tea.
Overindulgence in these agents, as with alcohol, affects the nerve cells and membranes, often causing severe attacks of headache.
Nervous headache is another common affliction. This seems to arise from several causes, such as impoverished blood and exhaustion from overwork of the brain. Hysterical headache is not uncommon. There is a severe kind of headache, the attacks of which appear first at early puberty and continue at intervals more or less frequent in women up to the change of life and in men to about the fortieth year.
The periodical headache is usually preceded by yawning, chilliness, languid, exhausted feelings, in others by peculiar emotional or mental activity. This is followed by unusual drowsiness, in which the night's rest is broken by dreams, and from which the patient awakes tired. Gradually, during the day, the headache develops, beginning in the eyes or bones over them. It gets more and more severe, shooting into the jaws and neck or extending to the back of the head and spine. As the pains get most severe, nausea or vomiting, often repeated, follow, in which the contents of the stomach, with mucus and bile, is ejected. The whole paroxysm lasts from five hours to two or even three days.
Neuralgic headache is a common variety; often the pain is not confined to the head, in fact neuralgia may affect almost any part of the system.