If natural sleep is the expression of a phase of decreased excitability due to the setting in of a tide of anabolism in the cells of the nervous system, what is the action of narcotics ?
If two poisons act on the same tissue, one stimulating and the other paralysing it, the paralysing substance removes the action of the stimulant substance, not by bringing the tissue back to its normal state, but by abolishing its excitability; hence, although life may be saved by such an action, yet it can only be so within certain limits of dosage, because the antagonism is never complete at every point.
Sleep is not exhaustion of the neuron in the sense that prolonged activity has reduced its excitability to zero.
In bronchitis with profuse expectoration the use of morphine is particularly dangerous, as it is likely to check the cough so necessary for getting rid of the secretion, but in the converse condition it usefully allays the harassing cough by diminishing the excitability of the respiratory centre.
The means of producing sleep may be divided into two classes: those (r) which lessen the circulation, and which (2) diminish the excitability of the brain cells.