When we review the various measures classed under the 1st, 4th, 5th, 6th, and 7th preceding heads, we are enabled to re-arrange several of the most important of them into new groups with definite pharmacodynamical properties and important therapeutical bearings. These groups are-(a) Expectorants; (b) Antispasmodics; and (c) Respiratory Sedatives.

a. Expectorants.-Expectoration, the discharge of the sputa, or secretions and other products of the respiratory passages, will manifestly vary with the amount and characters of the sputa, and with the expulsive force which can be brought to bear upon them. Measures are therefore called expectorants which increase the absolute amount of sputum formed, which so modify its characters as to facilitate its expulsion, or which evacuate it with greater ease: the first and second kinds of expectorants acting upon the glands, the third kind upon the muscular structures. Regarded otherwise, the expectorants will be found sometimes to stimulate the respiratory centre, e.g. Ammonia and Ipecacuanha, sometimes to depress it, e.g. warm, moist air. But of greatest practical importance is the action of expectorants upon the circulation; and according to their stimulating or depressing influence in this respect, they are commonly divided into (1) Stimulant expectorants, and (2) Sedative expectorants. It must be clearly understood that "sedative" and "stimulant" in this connection refer not to the respiratory, but to the circulatory effect of the bronchial measures.

(a) Stimulant expectorants include Ammonia, Scilla, all the Volatile Aromatic oils, Oleo-resins, and Balsams enumerated above; Strychnia, Alcohol, Senega, warm liquid food, and moderate exercise of the body generally or of the chest.

(b) Sedative expectorants include Alkalies, Iodides, Antimony; Ipecacuanha, and Tobacco; warm, moist air; and warm, moist applications to the chest-walls.

If we wished to construct other groups of expectorants we might add:

(c) Expectorants with a sedative effect on nerves.-These are chiefly obtained by combining other expectorants with Opium, e.g. Scilla and Opium, Camphor and Opium, Ammonia and Opium, Ipecacuanha and Opium-all of which combinations are officinal, Antimony and Opium, etc. Warm drinks have the same effect.

(d) Expectorants which alter the chemical composition of the sputa.-Tins is a highly important group. Alkalies increase the alkalinity of the sputa, and at the same time the water of the bronchial mucus, and thus the liquidity of the sputa. They constitute a special class called the Saline expectorants. Sulphur, Iodine, all the Aromatic Oils, Oleo-resins, and Balsams, are excreted, as such, or as their products, along with an increased flow of mucus; and most of these, especially the aromatic substances, have an antiseptic, deodorant, and disinfectant effect on the secretion, and on the surface from which they are given off. They may he classed as the Disinfectant expectorants. The water of the bronchial mucus is increased in almost every instance of increased secretion, hut specially by Alkalies, Iodine, and Antimony, which thus possess the valuable property of increasing the liquidity of the sputa. Lastly, Acids tend to diminish the amount of water, and thus the total amount of sputum, i.e. to "dry up" the secretion. They may he called anti-expectorants.

b. Anti-spasmodics.-These comprise a great variety of measures which have the common effect, directly or indirectly, of relaxing the muscular coat of the hronchi and the diaphragm. They are: (a) the various depressants of the respiratory branches of the vagus mentioned above (4a), such as heat, Iodides, Alkalies, etc. (b) The depressants of the other afferent nerves to the respiratory centre (5), especially warm applications to the chest-walls. (7) The depressants of the respiratory centre itself (6)-Alcohol, Ether, Chloroform, Opium, etc. (S) The direct nervo-muscular depressants-hronchial (4 d), such as Atropia, Tobacco, Amyl-nitrite, etc.; and parietal (7), Conium, etc. All these substances are distinctly depressant or sedative; hut we have still another group of bronchial antispasmodics (e), which are perhaps the most powerful of all, viz. some of the expectorants, such as Ipecacuanha, Senega, and Tobacco, which after momentarily increasing the spasm, cause a rapid and profuse flow of mucus from the bronchial wall, thus relieving the fulness of the vessels, provoking cough, and inducing expulsion of the cause of the spasm.

c. Respiratory sedatives.-These measures deserve a special name. The depressants of the afferent branches of the vagus to the brain, such as Opium, Ether, Chloroform, etc., not only act as antispasmodics and muscular depressants, i.e. prevent bronchial spasm, widen the tubes, and arrest cough, but also prevent or relieve pain and other distressing sensations referred to the respiratory organs. The most rational kind of pulmonary sedatives, however, are the expectorants above enumerated, in cases where the cause of the distress can he removed. A combination of the two classes will manifestly answer best in most instances.

III. Pathological Relations

The disorders and diseases of this system fall readily into two great classes, according as they affect (1) the respiratory element {the red corpuscle) and its circulation, or (2) the nervo-muscular apparatus, including the lungs and air-passages, the respiratory centre, and the afferent and efferent channels of communication. The first class were discussed in chapters viii. and ix.; the second will now be briefly noticed.

Circulatory, inflammatory, and degenerative changes comprise a large part of the diseases of the respiratory organs, such as bronchitis, pulmonary congestion, emphysema, and pleurisy, to which must be added new growths, whilst tuberculosis and syphilis occupy an intermediate position. Whatever their pathological nature, these diseases produce certain well-marked anatomical changes in the parts. The passages may prove to be obstructed, or actually occluded, by swelling of their mucosa, and by various products, such as mucus, pus, blood, or debris, which may be retained, inspissated, or possibly decomposed, thus irritating the nerves and vessels. Some of the bronchia may be entirely blocked, with collapse or consolidation of the corresponding lobules, and disturbance of the air pressure (emphysema) and blood pressure (hyperaemia) in the parts around. Portions of the lungs may be found either consolidated by pneumonia, or compressed by pleurisy, airless and functionless. Tracts of various size are frequently entirely destroyed by phthisis or gangrene. Haemorrhage may occur in the alveoli or passages. The right heart frequently proves to be secondarily enlarged, from disturbance of the venous circulation, the viscera congested, and the serous cavities and extremities dropsical.