the expiratory pressure exerted upon the contents of the alveolæ alone, it would readily overcome the spasmodic constriction of the bronchi, but it also compresses at the same time the bronchioles. "When the bronchi are spasmodically contracted, they are subjected during expiration to the general pressure of that movement plus the pressure of the spastic contraction of the bronchial muscles. The walls of the bronchioles being soft and compressible, the expiratory pressure, instead of overcoming the obstruction and opening them, would tend to close them all the more tightly." He calls attention to an analogous condition which obtains in capillary bronchitis, when, owing to swelling of the mucous membrane and to the accumulation of secretion in the tubes, the alveolæ are cut off. Here, too, the expiratory pressure is often sufficiently powerful to overcome the obstruction, but if under these circumstances it is too feeble, collapse of the lung ensues. When, on the other hand, the inspiration is strong enough to overcome this obstacle, air enters the alveolæ, and, being imprisoned there, causes inflation of the air-cells as in asthma. That collapse of the lung does not occur in the latter disease is due to the fact that the inspiratory act is always sufficiently powerful to overcome the spastic contraction of the bronchioles. [Footnote 13: A. Biermer, "Ueber Bronchial Asthma," _Sammlung klinischer Vorträge_, No. 12, Leipzig, 1870.] The air entering the lung during inspiration is pent up by the spastic constriction of the bronchi, which, acting as a valve, admits of its passage in one direction, but impedes its escape during expiration, and thus causes inflation of the air-cells and insufficient aëration. Owing to the distension of the alveolæ the thorax is expanded and the diaphragm forced downward. A tetanic spasm of the diaphragm lasting for hours, such as that which Wintrich describes, and with which he endeavors to explain the descent of that muscle as well as the other symptoms of asthma, is not only improbable, but is contrary to clinical experience. If the diaphragm were thus spasmodically contracted, it would remain fixed in one position, but Biermer has demonstrated that there is more or less rhythmic movement of that muscle even during the paroxysm; but if no movement of the diaphragm were observed, it would still be no proof of tonic spasm of that muscle, as its immobility might be due to other causes. According to Biermer, the inflation of the lungs and their insufficient ventilation afford a satisfactory explanation of the most important symptoms of asthma, as Breuer[14] has shown, in his paper on the automatic regulation of respiration through the pneumogastric nerve, that various embarrassments of respiration must be corrected by some suitable modification of the act itself; hence when, as in asthma, the lung is unable to empty itself, the expiratory act must be strengthened and prolonged to overcome the