This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
This experimental result is in contradiction to the teaching of clinical experience, which shows us that alkalies increase the amount of secretion, and render it more fluid. The results of clinical observation are quite as certain as those of Rossbach's experiments, for we may not only remark the greater quantity of expectoration, and its greater fluidity in persons taking alkalies, but we may note the alteration which they occasion in the amount and nature of the moist rales heard within the lungs. This can be observed most readily in persons suffering from phthisis, especially round the margin of the cavity. After catching a slight cold an extension of consolidation may be remarked, in which moist rales readily occur on the administration of dilute alkalies. When these are continued until the expectoration has been free for a day or two and the rales diminish, acids may be given with advantage, so as to dry up the expectoration still more. But if the acid is given too soon the expectoration diminishes, but the cough increases and becomes troublesome to the patient.
In all probability the difference between the results of clinical observation and Rossbach's experiments depends upon the difference of dose, the quantity usually given to a patient being proportionately much smaller than that which he employed. We are able to observe a similar difference between the effects of small and large doses in the case of iodide of potassium; a small dose of a grain and a half, taken by a healthy man three times a day, will almost certainly cause the nose to run freely, while if the dose be increased to ten, twenty, or thirty grains the excessive secretion will almost certainly be arrested.
The local application of one to two per cent. solution of sodium carbonate has very little action. The local application of strong liquor ammonias causes both congestion and increased secretion of mucus. Very strong solutions cause a croupous exudation from the surface of the mucous membrane. The local application of dilute acetic acid (three per cent. solution) has a similar action to weak solutions of ammonia : the mucous membrane becoming redder and secreting more mucus.
"When acetic acid was given internally, Rossbach observed in one case that the mucus, which was before watery and clear, became gelatinous and opalescent. This result agrees with what one finds clinically, that acids dry up the secretion and make it harder to expectorate.
Among astringents Rossbach tried tannin, alum, and nitrate of silver; the first two when locally applied made the mucous membrane appear paler by altering the epithelium and rendering it opaque, so that the vessels underneath could hardly be seen; at the same time they arrested the secretion of mucus almost entirely. A four per cent. solution of nitrate of silver also caused opacity of the epithelium, arrest of secretion, and dryness of the mucous membrane. There appears to be a difference in the action of nitrate of silver on the mucous membrane of the nose and on the trachea, as when the inside of the nose is touched by it, it causes a profuse secretion, whereas it causes dryness in the trachea.
The vapour of oil of turpentine mixed with air arrests the secretion of mucus, whilst a current of air alone, without admixture with oil of turpentine, will act as an irritant to the mucous membrane and increase secretion. Here again, however, a marked difference is to be seen in the effect of small and large doses, for when a watery solution containing from one to two per cent. of oil of turpentine was dropped directly on the mucous membrane, it became less vascular, but the secretion was at once increased, instead of being diminished, as it was by the vapour.
This action of oil of turpentine is of great therapeutical importance, inasmuch as in many cases of bronchitis we have profuse secretion with vascular congestion, a condition likely to be removed by the vapour of oil of turpentine.
Apomorphine, emetine, and pilocarpine, when given internally, all cause a great increase of the secretion of mucus, but they do not alter the vascularity of the mucous membrane. The most powerful of all these is pilocarpine, and after it come apo-morphine and emetine. One would therefore expect that pilocarpine would be the best remedy in catarrhal conditions, but this is not the case, for its other actions on the salivary and sweat glands and on the heart render its administration unpleasant for the patient. Sometimes also in children oedema of the lungs has followed its use. Apomorphine, on the contrary, has been found by Rossbach to be of the greatest service in catarrh of the larynx, trachea, and bronchi, both in adults and in children. Ipecacuanha has long been recognised as one of the most useful expectorants, but the dose given is often too small.
Rossbach's experiments have shown that the consequence of sudden changes of heat and cold applied to a part of the body is congestion of the respiratory mucous membrane with diminished circulation and stagnation of blood in the veins. A similar condition occurs in many cases of chronic bronchitis, and in them we not unfrequently find great benefit from vascular tonics such as digitalis, which, in addition to stimulating the vaso-motor centre, increase the activity of the heart, and thus tend to maintain the pulmonary circulation.
In what way cod-liver oil affects the bronchial mucous membrane it is perhaps hard to say, but there is no doubt whatever that it is one of the most efficient expectorants that we possess, and in cases of chronic bronchitis it affords more relief than any of the ordinary expectorants. It is possible that, being a form of fat which is readily assimilated, it is taken up by the young epithelial cells of the respiratory mucous membrane, and thus enables them to grow and maintain their attachment to the mucous membrane, instead of being at once shed in an undeveloped form as pus-cells in the expectoration.