378 DISEASES OF BEEATHING. 



on the supposition that, owing to some . sedative influenoe on the vaso- 

 motor nerves which supply the bronchial tubes, engorgement of the blood- 

 vessels of their mucous membrane takes place, with more or less blocking 

 up of the bronchial tubes. The vaso-motor nerves are the nerves which, 

 on becoming stimulated, cause contraction of the muscular coat of the 

 blood-vessels. Whichever theory we accept, we must, I think, regard 

 asthma as a nervous disease that is seldom if ever brought on by catarrh. 



The chief CAUSES of asthma are probably : bronchitis, foul air 

 in stages, and the breathing of air containing irritating vapours 

 or irritating particles. 



In order to warrant the decision that a case of difl&culty of 

 breathing is due to asthma, the existence of these paroxysms, 

 must be proved independently of any external exciting cause, such 

 as work, and after more or less regular intervals of ease, during 

 which the breathing is normal, to a greater or less extent. The 

 fact that the breathing in asthma, though difficult, is not hurried, 

 and that it is slower in expiration than in inspiration, serves to 

 distinguish this disease from bronchitis and pneumonia. Also, in 

 uncomplicated asthma there is little or no running from the nose, 

 except perhaps, at the end of a paroxysm. 



TREATMENT. — One of the best medicines in this disease is 

 chloral hydrate, which may be given by the mouth in a dose of 3 

 drachms dissolved in a pint of water. If there be difficulty in this, 

 inject hypodermioally (p. 644), 5 grains of morphia, or 1^ drachm 

 of chloral hydrate ; or inject into the rectum an ounce of chloral 

 hydrate dissolved in a quart of water. The precautions as to food 

 and sanitation recommended for broken wind (p. 376) may be 

 observed in cases of asthma. 



Asthma is a very serious unsoundness. 



Roaring. 



DEFINITION. — Roaring is a symptom of disease or malforma- 

 tion which gives rise to noisy and more or less distressed breathing. 



VARIETIES. — The chief varieties of roaring are as follows : — 



1. The paralytic form, which is the cause of about 95 per cent, 

 of cases of roaring. 



2. Roaring from mechanidal obstruction in the air •passages. 



3. Roaring from mechanical alteration of the shape of the air 

 passages. 



4. Roaring from poison. 



Any of these varieties may be either chronic or temporary. 

 When the noise of roaring is shrill, it is sometimes termed 

 whistling. 



