Active general congestion of the lungs has occasionally been observed in this disease, and has proved fatal in five minutes[81] and in an hour and a half[82] from the invasion of the symptoms. The rheumatic poison frequently excites pleuritis, some of the characters of which are--the suddenness with which free effusion occurs; the promptness with which it is removed, only perhaps to invade the other pleura, and then to reappear in the cavity first affected; the diffusion of the pain over the side and its persistence during the effusion; and its frequent concurrence with pericarditis, and in children with endocarditis; its little tendency to become chronic, and its marked proclivity to become double. It is often latent and unattended with pain. Sibson asserts that if in rheumatic pericarditis "pain over the heart is increased or excited by pressure over the region of the organ, it may with an approach to certainty be attributed to inflammation of the pleura," etc. The product of the inflammation is commonly serous, but occasionally purulent. [Footnote 81: _Thèse d'Aigue pleur._, 1866, par B. Ball.] [Footnote 82: M. Aran, quoted by Vasquez, _lib. cit._, p. 14.] The disturbances of the nervous system are amongst the most important complications of acute rheumatism, and are due either to functional disorder or very rarely to obvious organic lesions of the nerve-centres or their membranes. The dominant functional disturbance may be delirium, which is greatly the most frequent; or coma, which is rare; or chorea, very frequently observed in children; or tetaniform convulsions, which occur very seldom per se. As a rule, two or more of these forms coexist or alternate with or succeed one another, and the grouping, as well as the variety, of the symptoms may be greatly diversified. In 127 observations there were 37 of delirium only, 7 of convulsions, 17 of coma and convulsions, 54 of delirium, convulsions, and coma, 3 of other varieties (Ollivier et R., cited by Besnier).