[Footnote 93: Bright's case, 2, _Med.-Chirurgical Transactions_, xxii. 4; Dr. E. C. Mann, _N.Y. Medical Record_, 1875, 38; Bouilland, _Traité sur les Maladies du Coeur_, t. i. p. 33.] [Footnote 94: Leudet, _lib. cit._, p. 139; Dowse, _Lancet_, i., 1872, 9.] The causes of these disturbances of the nervous system, when not attributable to appreciable lesions, such as congestion, inflammation, hemorrhage, embolism, thrombosis, and softening, are not established. The following appear to be reasonable conclusions from the facts at present known: The most constant condition, and without which these cerebral symptoms very rarely arise, appears to be some susceptibility or vulnerability of the nervous system, inherited or acquired, rendering it apt to be disturbed by influences which less susceptible centres would successfully resist. Trousseau, who has especially advocated this view,[95] considered intemperance in the use of spirits to be a frequent source of this nervous predisposition. Accepting this neurotic predisposition as the factor generally present when acute articular rheumatism is complicated {41} with disturbances of the nerve-centres, we may inquire what are the circumstances in the disease capable of developing into activity the predisposition. [Footnote 95: _Clin.-Med._, Syd. ed., i. 513 _et seq._] Unquestionably, the existence of acute pericarditis, or of endocarditis, or of inflammation of the lungs or pleura, is one of those conditions. Probably hyperpyrexia acts in some cases as an exciting cause of the nervous phenomena, for while the delirium preceded the hyperpyrexia in 6 cases, it accompanied it in 19 and followed it in 10;[96] and the nervous symptoms disappear when the hyperthermia is removed by the employment of cold, and recur with the return of high temperature. The phenomena of sunstroke and heat-apoplexy prove that a high temperature is capable of producing convulsions and coma. That these grave cerebral disturbances are so infrequent in acute rheumatism (obtaining in about 3 or 4 per cent. only) is probably owing to the usual moderate range of temperature and the rarity of hyperpyrexia in the disease. Still, while hyperpyrexia is a disturber of cerebro-spinal function, too much importance must not be attached to it, for not only does such disturbance very frequently precede the hyperpyrexia, but there are many facts indicating that the hyperpyrexia is itself very frequently, like the delirium, tremor, and coma which precede or accompany it, but a consequence of disorder, usually of a paralyzing kind, of the nerve-centres. It has been met with in lesions of the pons, in tetanus, in injuries of the cord, in some cases of non-inflammatory softening of the brain and of cerebral hemorrhage; that is, in a class of affections not belonging to the specific fevers, but to those directly disturbing or destroying the functions of the nerve-centres. And cases of acute