This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
Narcotics are substances which lessen our relationships with the external world. They are closely related, as I have already stated, to stimulants; and alcohol in the various stages of its action affords us a good example of both stimulant and narcotic action. Alcohol at first excites the cerebral circulation and then begins to paralyse various parts of the brain in the inverse order of their development.
But this order differs in different individuals; for in watching the growth of children we find that the order of development of the nerve-centres in them is not always the same : some talking before they can walk, and others walking before they can talk. In all, however, the powers of judgment and self-restraint are among the last to be completely developed.
While the circulation of the brain is still active, the restraining or depressing effect of present external circumstances, and the restraining effect of training, during previous life, which are stored up as it were in the inhibitory centres, are lessened. The fancy is thus allowed free play and a condition of joyousness and volubility like that of a child occurs. The imagination and memory fail next in some, while the emotions become prominent, and to this follows paralysis or paresis of the power of co-ordination. In others the power of co-ordination is impaired before the mental faculties are much affected, the speech becomes thick and the walking becomes staggering and uncertain. At this stage reflex action still persists, but afterwards it is diminished, then abolished, and finally paralysis of the respiratory centre occurs. The effect of other drugs, such as ether and chloroform, is much the same as that of alcohol.
In the case of opium and Indian hemp, however, there is but little excitement of the circulation, and their effects appear to be due more to alterations in the relative functions of the different parts of the brain.
Belladonna, hyoscyamus, stramonium, and their allies, have a curious effect. They produce delirium of an active character, the patient having a constant desire to speak, move about, or be doing something, while at the same time he feels great languor. It is probable that this effect is due to the combined stimulant action of these drugs on the nerve-centres in the brain and spinal cord and their paralysing action on the peripheral ends of motor nerves.