Opium and Stramonium, classed among Narcotics, depress the function of this nerve as well as the nervous forces generally. So do other medicines similar to them. Opium in small doses allays irritability and diminishes spasm, and is then an indirect Expectorant; but in large doses it acts so powerfully as to render respiration difficult and expectoration impossible. Its use therefore demands great caution.
_True Expectorants._--The action of Antimony and Ipecacuanha upon the secretion of bronchial mucus is of so specific a character as to render it highly probable that these medicines add to their neurotic influence a true eliminative agency. We are as yet unable to decide whether or not they are ever secreted by these mucous glands, because not only is the analysis of the mucus a matter of difficulty, but hitherto no investigation of the matter has been made. Squill also is probably an Eliminative Expectorant.
Many of the true Expectorants are volatile and odorous in nature. All excreted substances have to pass by an endosmotic process through a thin animal membrane. And it is necessary before they can pass, that there should be on the other side of this membrane something which is capable of dissolving them. Diuretics are soluble in water, and they pass through into a watery fluid. But these Expectorants, whether they pass through the mucous glands, or immediately through the thin wall of the lung-cell, are brought directly into contact with air. And in this air these volatile matters are soluble, and are carried away by it.
This appears to be the reason why the Eliminatives which are volatile in nature tend particularly to act on the two aeriform secretions,--_i.e._ on that of the air-cells of the lungs, and on the common cutaneous transpiration. For though the glands of the mucous membrane of the lungs secrete mucus, yet the chief object of the terminal portion of that membrane is to absorb and secrete the gaseous matters of the blood. The following are the chief volatile Expectorants, the odours of which have been clearly detected in the breath of persons to whom they have been administered:--Turpentine, Camphor, Alcohol, Ether, and the volatile oils of Onions, Fennel, Asaf[oe]tida, Carraway, Cinnamon, and Anise.