INSOMNIA  , or deprivation of

sleep (Lat. somnus), a common and troublesome feature of most illnesses, both acute and chronic . It may be due to pain, fever or cerebral excitement, as in delirium tremens, or to organic changes in the brain . The treatment, when failure to sleep occurs in connexion with a definite illness, is part of the treatment of that illness . But there is a form of sleeplessness not occurring during illness to which the term " insomnia " is commonly and conveniently applied . It must not be confounded with occasional wakefulness caused by some minor discomfort, such as indigestion, nor with the " bad nights " of the valetudinarian . Real insomnia consists in the prolonged inability to obtain sleep sufficient in quantity and quality for the maintenance of health . It is a condition of modern urban life, and may be regarded as a malady in itself . It is a potent factor in causing those nervous breakdowns ascribed to " overwork." It may occur as a sequel to some exhausting illness, notably influenza, which affects the nervous system long after convalescence . But it very often occurs without any such cause . Professional and business men are the most frequent sufferers . Insomnia is comparatively rare among the poor, who do little or no brain work . It may be brought on by some exceptional strain, by long-continued worry, or by sheer overwork .

The broad

pathology is simple enough . It has been demonstrated by exact observations that in sleep the blood leaves the brain automatically .