The ETIOLOGY of this form of paralysis presents some peculiar problems. In all paralyses of the individual muscles we are obliged to invoke nerve-changes in special nerve-cells in the centres from which the individual nerves have their origin--changes along the course of the nerves; or, on the other hand, some myopathic change in the muscles themselves. In the muscles now under consideration we have a special function--namely, respiration--involved. The disorder is usually limited to these muscles alone. If it becomes general, it commences here. The phonators not being involved, it is probable that in a part of the cases reported the essential cause of the paralysis must be ascribed to disease in a centre in the brain, or at least along the course of the nerve near its origin. Other cases are evidently due to pressure on the pneumogastrics or recurrents. This view has been proposed by Bosworth. Von Ziemssen and others have thought that syphilis enters very largely into the pathology of this group of cases. There has been noted, as confirmatory of this proposition, that other symptoms of central disease have been in a few instances observed. Diseases affecting the recurrents have been known to affect these muscles alone: Ingals reports cases. On the other hand, it is quite certain that in a large majority of the cases recorded there has been no satisfactory cause assigned. In nearly all of the post-mortems there has been found a degeneration of the muscles. This is as we should expect to find it where the structures have been for a considerable time in a state of inaction. The histological change may possibly be in any case only the result of the paralysis, and not the cause of it. In a few instances there has been discovered a degeneration of the nerve-trunks by which the parts are supplied. As to the causes by which the muscles may become affected, we can imagine that the exposed position suggested by Mackenzie renders them peculiarly liable to mechanical injuries from hard substances forced down the oesophagus. They are subjected to changes of temperature produced by hot and cold drinks and food. Their relation to the seat of local inflammation of a specific as well as of a non-specific character renders them liable to become involved in morbid processes. The fact that the disease occasionally occurs after diphtheria, as I have in two instances demonstrated, gives additional weight to this hypothesis. The fact probably is that there are several varieties of the affection. The want of more accurate information as to the {88} previous history, as well as to the immediate antecedents of the attack, renders it impossible as yet to differentiate the cases due to one or other of these causes. For the present, then, we may conclude that paralysis of these muscles may depend upon either disease of the centres, disease along the track of the nerves, pneumogastric or recurrent, or to disease of the peripheral