This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
Lesser verified a markedly stimulant effect of small doses, both on the respiratory centre and on the pulmonary terminations of the vagi; large quantities, on the other hand, extinguish nerve-irritability in these parts. That the effect is directly on the centre is clear from its occurrence even after section of the trunks of vagi, but when these nerves are entire the effect is greater, so that they have some share in it. Small doses taken under certain conditions - as, for instance, by the Styrian mountaineers - render the respiration easier, less labored, and less hurried under severe exertion. On the other hand, even medicinal doses, if long continued, will induce in some persons a dyspnoea, allied to that of emphysema or even asthma, with dry cough or hawking of mucus. This I have verified several times in the subjects of eczema, observing its cessation with the omission of the drug, and its return under arsenical influence; there may be also hoarseness, coryza, tonsillitis, or even, according to some observers, bronchitis (McCall Anderson), probably from irritation excited in the bronchial mucous membrane by the elimination of the drug; it has certainly some special determination to the pulmonary tract. After large poisonous doses the dyspnoea is often urgent, and the respiration stertorous.