{197} 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] [Footnote 20: "Zur Kentniss des Bronchial Asthmas," _Virchow's Archiv_, Band liv., 1871.]