2. The Red Corpuscle

The Red Corpuscle. The red corpuscle as the great medium of external and internal respiration, as well as the prime mover of the respiratory centre, is an important agent through which the respiratory activity may be modified by food, drugs, and all the ordinary natural influences, studied in chapter viii (The Blood).

3. The Circulation

The Circulation. The corpuscles must be circulated by the heart and vessels, and any effect that we may produce upon these will greatly modify the respiratory functions. The pharmacodynamics of the circulation are discussed in the preceding chapter.

4. The Lungs And Air-Passages

The Lungs And Air-Passages. (a) The afferent or sensory nerves of the respiratory organs are stimulated by cold and dry air, Chlorine gas, Ipecacuanha, Senega, Tobacco, Nitre fumes, Ammonia, and Antimony. They are depressed or soothed by warm and moist air, warm food, warm applications to the chest wall; possibly by demulcent substances to a small extent; and by Opium, Chloral, Chloroform, and Ether. Sensations connected with the respiratory organs may be modified by the same means, the nerve-depressants thus proving to be pulmonary anaesthetics or anodynes, as well as interfering with reflex respiratory acts.

(b) The vessels of the bronchi may have the circulation through them increased by all measures which increase the activity of the circulation generally, viz. by purgation, exercise of the lungs, and bodily movement; by Digitalis, Scilla, Ammonia, Alcohol, Strychnia, and probably the whole series of Aromatic Oils to be presently noticed. Per contra, the bronchial circulation may be depressed by all cardiac and general vascular depressants, including heat, Alkalies, Iodides, Aconite, Antimony, and Ipecacuanha.

(b') The pulmonary circulation bears very complex relations to the respiratory movements, as regards the pressure and rate of flow in inspiration and expiration, ordinary and extraordinary. Manifestly as regards the general circulation, the pulmonary vessels may be modified by every influence which affects it, such as blood-letting, transfusion, purgation, a variety of drugs, and muscular rest or exercise. We possess one substance, non-officinal, which specifically contracts the pulmonary vessels, namely Muscarin, the active principle of the mushroom.

(0) Glands of the bronchi.-The secretion of bronchial mucus may be increased by alkalies, especially Ammonia; by Iodine, Sulphur, and Antimony; by Ipecacuanha, Senega, Tobacco, Scilla, and the great group of Aromatic Volatile oils, Oleo-resins, and Balsams, including Turpentine, Camphor, Benzoin, Copaiba, Ammoniacum, and the balsams of Peru and Tolu. Warm liquid food remarkably increases the bronchial secretion; on the contrary, cold dry food diminishes the bronchial mucus, as possibly do Belladonna, Stramonium, and Hyoscyamus, and certainly acids.

(d) The nervo-muscular structures of the bronchi and larynx are stimulated by those measures which act upon the afferent nerves (a) and perhaps they are also directly influenced by some of the same.

A group of substances of great therapeutical interest directly depress the same system, and so relax the bronchial walls and 2F-8 favour the movements of the respiratory air, viz. Belladonna, Stramonium, Hyoscyamus, Lobelia, and Tobacco; Opium, Chloral, and Cannabis Indica; Chloroform, Ether, Amyl-nitrite, and Iodide of Ethyl; Conium, and warm moist air.

5. Impressions reaching the respiratory centre through other channels than the vagus afford us a remarkably ready means of affecting it. Impressions may be stimulating, including irritation of the fifth cranial nerve in the nose by Ammonia, or on the brow by cold; of the olfactory nerve by odoriferous substances; of the optic and acoustic nerves by powerful light and sounds respectively; and of the nerves of the skin generally by painful impressions, such as flicking with towels, flagellation or slapping, extreme heat, mustard plasters, and other powerful local irritants. Or we may use measures with a sedative influence on the respiratory centre, including gentle warmth to the surface of the chest in the form of poultices and fomentations, warm baths, and local anaesthetics or anodynes, such as plasters and liniments of Opium, Belladonna, and Volatile Oils (Turpentine, Camphor, etc.) applied to the chest-walls.

6. The Respiratory Centre

The Respiratory Centre. Besides those influencing the afferent impressions, a variety of direct stimulants and depressants of this centre are in our possession. The force of the nervous discharges may be increased by Ammonia, Strychnia, Belladonna, Stramonium, and Hyoscyamus; probably by Ipecacuanha and Antimony temporarily; and by Alcohol, Ether, and Chloroform, for a brief period at the commencement of their action. On the other hand, the last-named drugs quickly diminish the force of the respiratory centre (Ether less rapidly than the others); and the same effect may be produced by means of Chloral, Opium, Aconite, Veratria, Conium, and Physostigma.

7. The Tracts of the efferent impulses from the respiratory centre, the Spinal Centres of the respiratory muscles, and the Nervo-muscular Apparatus of the chest and larynx may be stimulated, not only reflexly, but directly, by Strychnia, which greatly increases the vigour of the spinal centres; by electricity applied to the nerve trunks (phrenics, intercostals), or to the muscles directly; and by all measures which improve the nutrition of the nervo-muscular tissues, such as well-ordered exercise. Conversely, these parts may be depressed by physostigma, which greatly diminishes the vigour of the spinal centres; by Conium, which paralyses the motor nerves; and by Opium, which depresses the whole efferent mechanism. The use of these depressing measures is almost confined to the muscles of the larynx. Most powerful of all is the method of arresting, or at least controlling, the movements of the chest, by direct restraint, which is best accomplished by means of strapping or bandaging.