URJEMIA. — The dyspncea occurring as a symptom of urmia is more or less continuous and accompanied by presence of casts in the urine.
Etiology. — Heredity shows itself in about one-half of the cases when three generations are included in the compu tation.
The influence of heredity is very great; the absence of asthma in the family his tory greatly increases the chances of cure. Dauchez (Revue Mensuelle des Maladies de l'Enfance, July, '94).
[If collateral diseases dependent upon an arthritic diathesis, rheumatism, gout, migraine, etc., are included as predis posing factors, as taught by Trousseau, almost every case will be found to be hereditary. SAJous.] Asthma presents itself before the age of ten years in one-fourth of the cases, but it may occur at any period. It is more frequent among males than among females. The wealthy are more prone to it than the poor, owing to dietetic errors and sedentary habits, the latter cause also explaining the disease's pre dilection for persons deprived of phys ical exercise, such as clergymen, lawyers, clerks, etc.
Atmospheric influences are active factors in the production of an attack. Excessive dryness, such as that of over heated or insufficiently ventilated rooms, or, on the contrary, excessive dampness may bring on a paroxysm. Cases which a rheumatic diathesis exists are especially sensitive to dampness.
A patient living on one side of the street may be exempt from asthma, while on the other he may be affected. This may be due to the fact that on one side he lives in a shady room, and on the other in a sunny one. This is a factor of no small moment, in not only the asth matic, but in all subacute and chronic bronchial disorders. J. B. Walker (Re port of Amer. Climat. Soc., Boston Med. and Surg. Jour., Nov. 17, '93).
Asthma, and the predisposition thereto, depend upon four causal factors. Tendency to (1) bronchial spasm (in creased tone of the bronchial muscles), (2) vasomotor insufficiency (decreased tone of vascular musculature), (3) con gestive hypermia of the respiratory mucous membrane, and (4) an abnormal specific secretion from the same. These
four factors may be influenced by the peripheral nervous system, the con stituents of the blood, or the cerebrum, especially the cortex; thus, asthma may be peripherigenic, llinatogenic, or psy chogenic and cerebral. Sillle (Wiener Woch.. Jan. 22. 1903).
Pathology. — Various theories have been propounded to explain the dysp ncea, but the prevailing one to-day is that it is due primarily to spasm of the smaller bronchi, as taught by Laennec, Biermer, and Williams, and, secondarily, by spasm of the muscles of the thorax and of the diaphragm, which are unable to cause expulsion of the air imprisoned in the alveoli on account of the restricted lumen of the bronchi.
[The reduction in the number of res pirations would tend to demonstrate that the resistance to the egress of air is the main cause of the difficulty. The expired air shows an increase of about 10 per cent. in carbonic acid. It contains little or no oxygen in marked cases, the blood having absorbed all that contained in the increased residual air. This com pensatory effort is not sufficient, how ever, to satisfy the demands of the sys tem for the oxidation of the tissues. Im perfect action of the chest-walls is often due to momentary paresis of their mus• cular supply induced by the absorption of CO, SAJous.] Primary spasm of the bronchial mus cles leads to a subsequent temporary paralysis, by which the increased demand on the external muscles and the dyspnoea is prolonged. Spasms of the bronchial muscles render the muscles of expiration for a long time incapable of performing their functions. Cameron (Brit. Med. Jour., June 1, '39).
[The theory of Salter—that the tem porary contraction of the bronchi giving rise to the dyspncea is due to spasm of the circular muscular fibres of the bron chial tubes—is losing ground. SAJOITS.1 That the spasm depends upon the con tractility of the circular muscular fibres of the bronchi and that it is essentially spasmodic in character is the only view by which the phenomena of the disorder can be adequately explained. Wilson Fox (Times and Register, Apr. 2, '92).