[Footnote 21: Not being able to obtain the original paper, the writer is indebted for the greater part of what he has written in regard to the Leyden theory to the treatises on asthma by Knauthe in _Eulenburg's Encyclopædie der gesammten Heilkunde_, and by Riegel in the work already quoted.] Of the different theories of bronchial asthma which have just been presented, that of Biermer, although unsatisfactory in many respects, offers the best explanation of the pathology and symptoms of that disease. PATHOLOGICAL ANATOMY.--Bronchial asthma being a purely functional neurosis, the organs involved present no anatomical changes specially characteristic of that affection. It is true that in cases of long standing, in which, owing to oft-repeated attacks, the air-cells have become distended and their walls attenuated, we find the lungs in the condition which will hereafter be described as emphysema, but these, as well as the evidences of chronic catarrh observed in these cases, are due to the secondary affections, and not to the primary disease. As previously stated, a certain amount of hyperæmia of the mucous {198} membrane of the larynx, trachea, and bronchi may be observed during life with the aid of the laryngoscope; but whether this condition leads to permanent tissue-changes observable after death is exceedingly doubtful. In the pneumogastric nerve pathologists have as yet been unable to discover, either at its origin or along its course to the lungs, any alteration in structure capable of explaining the phenomena of bronchial asthma. DIAGNOSIS.--The suddenness of the attacks; the occurrence of the paroxysm usually in the latter half of the night; the slow, labored expiration, with the whistling, wheezing sounds which accompany it; the expectoration of catarrhal sputa toward the close of the attack; the normal respiration and absence of all signs of disease during the interval between the paroxysms,--are the features by which a case of simple uncomplicated asthma may be readily recognized. When these symptoms are present in their integrity in an otherwise healthy subject, there is no difficulty in arriving at the diagnosis; but, unfortunately, the picture is not always complete. The asthma may be complicated with organic disease of the heart or lungs, while primary disease of these organs, as well as certain affections of the nervous system, may produce symptoms closely resembling those of bronchial asthma, and from which it is very essential to distinguish them. The following are some of the affections which may be mistaken for bronchial asthma: 1. Bronchial catarrh may be accompanied with more or less difficult respiration, but even in its worst forms it never causes the severe attacks of dyspnoea observed in bronchial asthma, and, as Riegel justly remarks, the severity of the symptoms in the latter disease are out of all proportion to the insignificance of the physical changes.