DIPHTHERIA. — From the Greek: (4)04a, a skin or membrane.
Definition.—Diphtheria is an acute infectious and contagious disease pro duced by the presence and development of the Klebs-Loeffier bacillus. As it occurs in man, it is usually characterized by the presence of false membranes upon the surfaces primarily attacked, espe cially the mucous membranes of the nose, pharynx, larynx, or trachea. There can no longer be any question of the specific relation between the great ma jority of cases of the disease known since the time of Bretonneau as diphtheria and the bacillus with which Klebs and Loeffler have identified their names. The bacillus is regularly obtained in cultures from affected throats; it can readily be isolated; and when pure cult ures are injected in animals they repro duce the essential features of the disease met with in man. Welch and others, by inoculating the mucous membranes of guinea-pig-s, have even succeeded in producing the false membranes so closely associated with the disease in man. All the constitutional effects and character istic lesions, except the formation of membrane of diphtheria, have likewise been produced by the injection in ani mals of the toxins produced by the spe cific bacillus. In experimental diph theria, induced either by the injection of cultures of the Klebs-Loeffier bacillus or of its toxins, the most striking feature is the production in animals of the paralyses due to nerve and muscular de generations, such paralyses reproducing most exactly' the phenomena so often observed in clinical diphtheria. This feature of the experimental process has so impressed itself upon those most in terested in laboratory researches that some propose to define diphtheria as an acute infectious disease, produced by the action of the Klebs-Loeffier bacillus, and characterized by,' the development of nerve-degenerations.
While this teaching may be most in harmony with the combined evidence of clinical observation and laboratory re search, it does not yet seem advisable to so far depart from the conceptions of diphtheria which have heretofore ob tained. The appearance of false mem _ brane has long been regarded as almost diagnostic; it still belongs to the great majority of cases, and can readily be appreciated, while the nerve-degenera tions, if they appear at all in clinical diphtheria, are met with only in the later stages of the disease, long after the question of diagnosis will have been de termined.
Varieties.—The classification of the acute inflammations affecting nose, throat, etc., has not yet reached a satis factory stage. The distinctions based upon the presence or absence of pseudo membranes have lost their significance.
While the great majority of pseudo membranous inflammations of these parts are due to the action of the diph theria bacillus, a considerable number of such inflammations are produced by the action of other bacteria, especially the streptococci and staphylococci. On the other hand, the action of the diph theria bacillus is not always attended by the production of pseudomembranes. The intensity of the local action of the bacilli varies greatly, and it has been found that this diphtheria bacillus may be the cause of simple inflammatory processes, formerly designated as catar rhal, which present no appearance of false membranes. Moreover we find that the all-important question in any case, both with reference to prognosis and treatment, is the presence or absence of the diphtheria bacillus. We, therefore, abandon the former classification into catarrhal and pseudomembranous proc esses and speak of:— 1. Diphtheria, or true diphtheria, in which we include all cases of acute in flammations affecting mucous mem branes associated with the presence of the diphtheria bacillus in sufficient number to constitute a probable causa tive agent. Thus, if a culture from a sore throat show the presence of the diphtheria bacillus, that case is at the present time accepted as diphtheria, whether there be or not pseudomem brane present, and no matter what other bacteria be associated in the culture with the diphtheria bacillus. It must, how ever, be noted that the presence of the diphtheria bacillus without further clin ical evidence does not constitute diph theria any more than the presence of pneumococci in the mouths of healthy persons constitutes pneumonia.