This is a diseased state of the lungs, marked by paroxysms of difficult breathing and distress, accompanied by a wheezing sound. It is believed to be due to spasmodic contraction of the bronchial tubes, and from the peculiar suddenness of its appearance and disappearance it partakes of the character of a nervous disorder.
These are very obscure, but seem to be connected in some instances with digestive disturbance, and by some authors are placed in the category of diseases of the digestive system. In susceptible animals it may be induced by breathing an atmosphere charged with irritating gases and other impurities. Besides a vitiated atmosphere, it is sometimes brought into existence by an attack of bronchitis, which is undoubtedly a factor in its development.
The attacks may come on so suddenly that warning symptoms are brief, if at all observed. The breathing is at once difficult and distressing, and the duration of the attack altogether uncertain. Inspiration is less difficult than expiration, the latter being accomplished with a double action of the flank, and the whole body receiving a distinct jerk at the end of the movement. As compared with broken wind, which in some respects it resembles, the symptoms are more paroxysmal and acute, there is also greater distress, as evidenced by the anxious countenance, and the short irritable cough, which returns again and again in choking paroxysms. The discharge of small quantities of mucus as a result of coughing, and more or less elevation of temperature and loss of appetite, also serve to distinguish asthma from broken wind. Its sudden appearance is as remarkable as its rapid subsidence, but in some cases, after repeated attacks, it passes imperceptibly into that form of lung disease, known popularly as "broken wind". The subject of asthma is pretty sure of a recurrence of the affection at no very distant date.
An oily aperient, preferably linseed-oil, may be given first, and followed at short intervals with fairly large doses of such sedatives as chlorodyne, or camphor and belladonna, combinations of stimulants, as nitrous aether and valerian, and failing early relief a change of sedatives to chloral and the bromides of potassium and ammonium. Chlorodyne is especially useful, and rather bold doses are found to be safe and speedy in effect. All dry and dusty food should be removed, and no bulky aliment allowed. Linseed, boiled or scalded, is found to be the best food, and undoubtedly has a medicinal effect also. This, with a little bran and scalded oats, should be given in small quantities, and often. Different animals are differently affected by atmospheric conditions. Some experience relief in a moist air, while others are benefited by dryness. Cold air is always prejudicial. In dealing with this disease the effect of warm vapour should always be tried, either by means of a nose-bag containing moist bran or by allowing a pail of steaming hay to stand near the patient's head. To guard against a recurrence of the disease the dietary should be carefully regulated, and an oleaginous aperient administered every few weeks, according to the state of the bowels.