2. The influences associated with the different critical periods of life;
3. The influences attached to sex;
4. The action of constitutional diseases, such as phthisis, anæmia, gout, syphilis, diabetes, nephritis, malarial poisoning, metallic poisoning.
The most important of the second group of causes are—
1. Atmospheric influences and the local action of heat and cold;
2. Injuries and irritation of nerves;
3. Irritation of related nerves (so-called reflex and sympathetic neuralgias);
4. Acute febrile diseases.
In most cases more than one cause is to blame, and each should be separately sought for.
PREDISPOSING CAUSES.—1. Hereditary Tendencies.—It is generally admitted as beyond question that neuralgias are most common in families in which other signs of the neuropathic taint are prominent. Such affections as hysteria, neurasthenia, epilepsy, asthma, chorea, dipsomania, and even gout and phthisis as it would seem, are akin to the neuralgic tendency.