obstruction occasioned by the spasmodic constriction of the bronchial tubes; whereas incomplete filling of the lung would necessitate increased inspiratory effort. According to Biermer, "expiratory dyspnoea is as characteristic of obstruction of the finer tubes," be it from spasm, as in asthma, or from stoppage with viscid mucus or from swelling of their lining membrane, as in bronchitis, as the same condition during inspiration is of narrowing of the larger air-passages--an important point in differential diagnosis to which we shall again have occasion to refer. He is unable to explain the relationship between bronchial spasm and catarrhal hyperæmia of the air-passages, but believes that it may be accounted for as follows: "Either the bronchial fluxion causes the spasm--that is, that there exists between them a causal connection--or the hyperæmia and the spasm are the {196} joint effect of the exciting (centripetal) nerves; in other words, both are due to reflex action."[15] [Footnote 14: "Die Selbsterneurung der Athmen durch den N. vagus," _Sitzungsbericht der K. K. Akademie der Wissenschaften zu Wien_, Bd. lviii. Abtheilung ii., Nov., 1868.] [Footnote 15: In presenting Biermer's theory the writer has drawn freely upon that author's well-known lecture on "Bronchial Asthma," as published in _Volkmann's Sammlung klinischer Vorträge_, _loc. cit._] Another explanation of the phenomena of asthma is that proposed by Lebert,[16] who, although he concedes that bronchial spasm is an all-important factor, denies that it of itself is sufficient to account for the sudden and enormous inflation of the lungs observed in that disease. He doubts the possibility of a valvular closure of the bronchi, as claimed by Biermer, but believes that the bronchial spasm, which he regards as primary, causes secondary spasmodic contractions of the diaphragm and of the inspiratory muscles of the neck and chest. The spasm of the diaphragm he believes to be tonic in its character, but not continuous, thus meeting Biermer's objection to the Wintrich theory, that tonic spasm of that muscle lasting longer than a few minutes would inevitably cause fatal asphyxia. [Footnote 16: _Klinik der Brustkrankheiten_, 1ster Band, 2te Hälfte, p. 438.]