There appears also to be a specific action of lowering the reflex excitability of the spinal cord.
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.
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.
This nervous excitability was inherited, though' not to the same excess, by Octave, whose mother died in his infancy and left him to the care of the hypersensitive invalid.
Amongst those which lessen excitability of the brain-cells are opium, morphine, hyoscyamus, chloral, sulphonal, trional, paraldehyde, chloralamide, chloralose, hop and many others.
Sleep is not exhaustion of the neuron in the sense that prolonged activity has reduced its excitability to zero.