There is quite a difference among authorities as to the place in the classification of disease of the larynx which should be assigned to spasm as met with in childhood, and which is also occasionally encountered in adult life. It is not possible, perhaps, in the present state of knowledge, to separate in every instance those cases in which there is disorder of the circulation and nutrition of the larynx from those in which the spasm is the result of disturbance simply of innervation, or in other cases the reflex manifestations of nervous irritation elsewhere. Generally, however, this can be done. I have for a long time been accustomed to consider the affection known as spasmodic croup to be a mild inflammation of the larynx, and that it differs from the same affection in the adult for the reason that the lumen of the tube is smaller, the cartilages are more yielding, and the susceptibility of the parts is greater, and further for the reason that the nervous system in childhood is always more prone to spasm than in the adult. Stridulous laryngitis, however, is a real disease, and is for the reasons above given a neurosis, even though it is an inflammation. It is entitled to a separate description for the reason that the symptoms are so well marked and differ in so many particulars from those of ordinary inflammations. That there is, besides, a true spasm of the muscles of the larynx, independent of inflammation, by which the vocal cords and the constrictors are brought into action and possibly kept in a state of tonic contraction, is possible. In a majority of instances of laryngeal spasm there is a degree of inflammation, as above stated, or at least a degree of congestion of the mucous membranes. It is certainly true, however, that in exceptional cases there are no indications of such a condition of the parts, so far as we can determine by ante- or post-mortem study. It seems to be evident, then, that under this name of spasm of the larynx or of some synonym of it many careful observers have recorded facts and have grouped them with the thought that the functional derangement was the main trouble. The real difficulty appears to be that the spasm is in fact a symptom--a symptom of perhaps several different disorders, but so prominent and creating so much alarm that it has seemed for the time being to be the disease itself; and yet in most cases there is a mild form of inflammation, local in its extent, and producing, so long as there is no interference with the function of respiration, no general disturbance. It is perhaps appropriate to include in the discussion not only the purely nervous cases, but also those conditions in which, while there is hyperæmia, and probably always some derangement of secretion, nevertheless the symptoms and dangers concern mainly the motility of the muscles of the organ.