The results of auscultation and percussion in ordinary bronchitis, limited to the membrane lining the larger bronchial tubes, are mostly negative. In some instances during the first or dry stage, the respiratory or vesicular murmur may be slightly harsher or more dry than natural, and after the exudation or secretion of mucus, as indicated by expectoration, there may be some coarse, moist râles, which are removed temporarily by coughing, but return again in a little time. These râles are heard much more in cases occurring either in infancy or in old age than in youth or the middle period of adult life. Percussion elicits only the natural degree of resonance throughout the whole course of the disease, except in those rare cases in which complete occlusion of the bronchial tube has taken place, causing exclusion of air from certain lobules of the lungs, and consequently a shade of dulness on percussion over such lobules. Mechanical Bronchitis. By mechanical bronchitis is meant those cases in which the inflammation is caused by the direct action of mechanically irritating substances floating in the inspired air, as fine particles of steel and other metals, particles of stone, charcoal, and various vegetable powders and fungi. Such substances, when inhaled, are liable to impinge on the surface of the bronchial membrane and produce direct irritation and inflammation, both acute and chronic. Cases originating from this class of causes differ from ordinary acute bronchitis chiefly in the mode of beginning and in the greater tendency to continue in the chronic form. Instead of slight rigors, coryza, and early development of moderate general fever, the patient generally complains first, and for several days, of a sense of tickling or fulness in the air-tubes, with occasional paroxysms of violent coughing and little expectoration. Sometimes particles of the foreign substance that is producing the inflammation may be seen mixed with the mucus or matter expectorated. In many of these cases there is much soreness in the chest and considerable dyspnoea, especially during the night, followed by severe coughing in the morning, and a more free discharge of mucus occasionally containing little streaks of blood, but which is never intimately intermixed with the sputa as in pneumonia. If the patient, by change of occupation or otherwise, ceases to be exposed to the further action of the exciting cause, the symptoms soon begin to abate, and a complete recovery may take place in from two to four weeks. If exposure to the further action of the exciting cause is not avoided, the disease will necessarily assume a chronic form, and in many cases produce such changes as to materially shorten the life of the patient. {171} Capillary Bronchitis.