(c) Acute disseminated non-suppura tive encephalitis has no distinct clinical existence. It may occur as a result of syphilis. or during the covirse of the acute infectious diseases, as typhoid and typhus fever, erysipelas, scarlet fever, diphtheria, small-pox, influenza, septi cmrnia, and pymia. Pathologically, small foci of inflammation appear quite early distributed throughont the brain.
Colonies of micrococci have been found scattered throughout the brain. This condition has been termed mycosis of the brain. The symptoms produced by these lesions must vary indefinitely with their number and distribution. The cases reported are too few to base any clinical description upon.
Although acute non-suppurative en cephalitis has been established as a clin ical type by the studies of many well qualified observers, its etiology is still largely a matter of speculation. It is true that we know something of the con ditions favorable to its development, but why the affections which give rise to it at times are not more frequently fol lowed by this disease, when it is consid ered that they are very common dis eases, is hard to explain. It can be stated that at present we are almost wholly ignorant of its primary causative factor, and the exact mode of produc tion of the inflammatory lesions.
Etiology.—Acute non-suppurative en cephalitis in its focal manifestations most frequently occurs in connection with some acute infectious disease. It may arise during the progress of the infective process, or days or weeks after convalescence has been established. The diseases with which it has most fre quently been associated are influenza, the acute infectious diseases of childhood, typhoid fever, and diphtheria. Certain cases occur in which these infections are absent. This fact has been explained by some writers upon the subject as pointing to the probable existence of a definite toxin peculiar to the disease. Leichtenstern and ICauwerck believe that the focal-hxmorrhagic form of acute en cephalitis may be of bacterial embolic origin. The latter observer, with Pfuhl and many others, think that the nervous symptoms may be the first sign of the in fection. Traumatism may be a cause of both focal and diffuse encephalitis, but is far more frequently causative of the latter. The same may be said of alcohol and syphilis.
Acute non-suppurative encephalitis of all varieties is far more frequent under the twentieth year of life, and the ma jority of cases of acute focal encepha litis occur during infancy and childhood. After the age of twenty alcohol, syph ilis, traumatism, and the influenza in fection are the chief causes recorded. It
has also been known to follow sun-stroke.
few autopsies which have been made in cases of acute non suppurative encephalitis show in the acute focal lesions the presence of the ordinary appearances of acute inflam mation of brain-tissue, and very com monly associated with numerous punc tate haemorrhages within the affected areas. The patches may be small, sin gle or multiple, and either confined to a small portion of one lobe or more or less diffused throughout one region of the brain. Macroscopically the acute le sions are reddish gray in color, of dimin ished consistexce, sometimes amounting to acute red softening, and are sur rounded usually by an area of increased vascularity, showing lesser degrees of the inflammatory process nntil normal brain tissue is reached. In sorne cases the process is sharply defined, but no dis tinct limiting membrane has been de scribed. The htemorrhages, which are common in these cases, are -usually small and punctate in form, but may be large and attended by- disintegration of the brain-tissue in their immediate neigh borhood. Microscopically these lesions present the evidences of an exudative inflammation. The vessels are seen to be ruptured here and there, an exodus of leucocytes is seen especially marked about the vessels and often distending the perivascular lymph-spaces, while granular cells are apt to be present.
Upon microscopical examination in acute cases of this kind, aggregations of large round or angular epithelioid cells constantly found: these cells exhibit a great tendency toward fatty degenera tion. Friedmann (Ncurologisches tralblatt, Aug. 1, '90).
The parenchymatous changes arc probably secondary to the vascular le sions, and broken-down cells and disin tegrated nerve-fibres are seen when the inflammatory process has prog,ressed far enough to destroy these elements. The role of the infecting microbes in the cases arising from infectious diseases is still a question. Whether they operate directly from the blood upon the tissues or whether the lesions are due to some toxin generated by them is undeter mined. When basal structures are at tacked, the cranial-nerve roots have been found to be affected by inflammatory changes resulting in degeneration or softening. The membranes are fre quently implicated when the inflamma tion is cortical, and may present bright reddish patches due to distended vessels and minute Illemorrhages.