There appears also to be a specific action of lowering the reflex excitability of the spinal cord.
Sleep is not exhaustion of the neuron in the sense that prolonged activity has reduced its excitability to zero.
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 ?
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.