16 Klinik der Brustkrankheiten, 1ster Band, 2te Hälfte, p. 438.
Theodor Weber,17 rejecting the above theories on the ground that neither bronchial spasm nor tonic contraction of the diaphragm is capable of explaining why catarrhal secretion should come on at the close of an attack in which at the commencement there was no catarrh, attributes the phenomena of asthma to sudden swelling of the bronchial mucous membrane, the result of dilatation of its blood-vessels produced through the agency of the vaso-motor nerves; thus reviving the fluxionary theory of Traube. In support of this theory he cites the result of Von Loven's18 experiments, which prove that irritation of the sensory nerves is followed by reflex engorgement of the territory to which they are distributed. Weber considers that this engorgement of the bronchial mucous membrane is somewhat similar to the acute swelling and stoppage of the nostrils to which many persons are subject—a closure which often does not last longer than a few moments, and which is attended with increased redness and swelling of the Schneiderian membrane. The mucous membrane of the nostril and that of the bronchi being both parts of the respiratory tract, and somewhat similar in structure, he concludes that the process in the nostrils is analogous to that which occurs in the bronchi during the asthmatic paroxysm. As additional proof of the correctness of his hypothesis he cites the fact that such occlusion of the nostrils is often the precursor of the asthmatic attack, and in some cases continues throughout the paroxysm. See investigations of Daly, Roe, Allen, and Hack, further on.
17 "Ueber Asthma Nervosum," Tageblatt der 45 Versammlung deutscher Naturforscher u. Aertze in Leipzig, etc., 1872, p. 159.
18 Naturforscher u. Aertze in Leipzig, etc., 1872, p. 159.
The idea that asthma is due to swelling and engorgement of the bronchial mucous membrane appears to have been confirmed by the tracheoscopic observations of Stoerk.19 On examining the air-passages with the laryngoscope, he could see the mucous membrane of the trachea as far as visible (that is, to the bifurcation) grow red with the onset of the paroxysm, and resume its normal appearance after the termination of the attack. He opposes the spasm theory, denies the correctness of Biermer's conclusions, and adopts Weber's explanation of the asthmatic phenomena. He agrees with Wintrich that spasm of the diaphragm occurs, but claims that it results from the tension to which it is subjected by the inflated alveolæ: the diaphragm being forced downward by the distended lung, its fibres are stretched, and the result is a tonic spasm of that muscle. His objections, although well stated, are not sufficiently conclusive to cause us to accept his opinion in preference to that of Biermer and other supporters of the spasm theory.
19 Mittheilungen über Asthma bronchiale, etc., Stuttgart, 1875.
Max Schaeffer maintains that asthma is due to bronchial fluxion, as advocated by Weber, but claims that the hyperæmia is followed by spasm of the bronchial muscles, the former being primary and the latter secondary. He also, with many other recent writers, believes that asthmatic attacks are often associated with pathological conditions in and about the upper air-passages, such as naso-pharyngeal and laryngo-tracheal catarrh, polypi, hypertrophied tonsils, and enlarged cervical glands; all of which act as irritants, which, being transmitted through the neighboring nerves to the vagus, induce the bronchial spasm.
Among the older and discarded theories is that of Bree, who in a work published at the commencement of the present century expressed the opinion that the dyspnoea of asthma was simply an effort on the part of nature to rid the bronchial tubes of an irritating substance supposed to have accumulated in them previous to the attack. He believed that this materia peccans was thrown out with the expectoration which occurs toward the close of the attack. He regarded the violent efforts made by the respiratory organs to expel this offending substance from the bronchial tubes as similar to the tenesmus of dysentery or the painful contractions of the bladder when irritated by a rough calculus. Bree was unable to define more clearly the nature of this offending substance, but of late years another writer, Leyden,20 has discovered in the sputa of asthmatics certain peculiar crystals to the irritating effects of which he attributes the various symptoms. These crystals had been observed previously by Charcot in the blood of leukæmic patients, and subsequently by Neumann in the medulla of the bones of patients who had died of that disease. Leyden describes the expectoration in asthma as tough, grayish-white, and very frothy. Imbedded in a transparent hyaline mass are a number of small bodies, some thread-like, others in the form of little plugs or flakes. Under the microscope these little bodies are found to consist of a mass of brownish cellular detritus containing large numbers of crystals. These are colorless, octahedral in form, with sharp points, and vary greatly in size, some of them visible at once, while others are seen only with the highest powers of the microscope. Their composition has not been determined, but is supposed to be a substance resembling mucin. Leyden's idea is that the sharp points of these octahedral crystals irritate the terminal ends of the pneumogastric nerve in the mucous membrane of the bronchi, and that this irritation, being transmitted to the nervous centre, is reflected back, and thus causes spasm of the bronchial muscles. It seems, however, that these crystals are not peculiar to bronchial asthma, having been also found in chronic catarrh and other affections of the bronchi.21
20 "Zur Kentniss des Bronchial Asthmas," Virchow's Archiv, Band liv., 1871.
21 Not being able to obtain the original paper, the writer is indebted for the greater part of what he has written in regard to the Leyden theory to the treatises on asthma by Knauthe in Eulenburg's Encyclopædie der gesammten Heilkunde, and by Riegel in the work already quoted.