On auscultating the chest it will be found that the ordinary vesicular murmur is either entirely absent, or if heard it is only over very limited areas. In the place of it we have an endless and ever-changing variety of dry sounds, such as whistling, cooing, mewing, snoring, etc., technically styled sibilant or sonorous ronchi. They are usually equally diffused over both lungs, but are sometimes confined to one. The sibilant râles afford an index of the degree of spasm, being in mild cases equally audible during both inspiration and expiration, while in severe attacks they are louder during expiration (Biermer). That the vesicular murmur cannot be heard is due not only to its being masked by the louder ronchi, but also to the absence of the condition necessary for its production, the spasmodic constriction of the bronchial tubes or their plugging with tough, viscid mucus preventing the entrance of sufficient air to produce the sound. Sometimes a hitherto occluded tube becomes pervious, and we have vesicular respiration where a moment before only dry sibilant râles were heard. Usually at the close of the attack, when cough sets in, there are occasional moist râles. These become more frequent as the expectoration becomes more abundant. Frequently, however, the paroxysm terminates much more abruptly, the spasm relaxes, and the air rushing through the tubes gives rise to puerile respiration. During the paroxysm there is, even in the early stages of asthma, more or less distension of the lungs, measurement of the chest showing that its circumference is four to eight centimeters greater than before the attack (Beau). This transitory emphysema, which must not be confounded with that due to structural changes observed in old cases, disappears with the attack, and the lung returns to its normal condition. This distension causes the exaggerated resonance obtained by percussion which is one of the most constant symptoms. At the base of the lung, especially posteriorly and laterally, there is a peculiar modification of the percussion sound to which Biermer has applied the name Schachtelton, from its resemblance to the note produced by striking {188} an empty pasteboard box. Besides this exaggerated resonance, it will be found that the line of dulness on the right side, which marks the upper border of the liver, is fully two inches lower during the paroxysm than before, and that the area of cardiac dulness is somewhat diminished by the overlapping of the distended lung-tissue (Riegel). Another peculiarity elicited by percussion, and to which Bamberger was the first to direct attention, is that in some rare cases instead of moving vertically the line of hepatic dulness remains unchanged during both acts of respiration.