Gangrene of the lung is very seldom recovered from, but, unless the diagnosis from examination of putrescent sputa has been at fault, there have been cases in which, with the limited destruction of the affected lung, it was not fatal. Pseudo-membranous croup destroys life in the majority, but not in nearly all the cases of its occurrence. It is most likely to end in death when distinctly a part of an attack of epidemic or endemic diphtheria. {168} Valvular heart lesions were formerly regarded as incurable, in the sense of restoration of the normal condition and action of the valves impaired, yet not incompatible with years of life. This restoration certainly very seldom takes place. But the experience of many close observers leads to caution in anticipation of necessary and permanent disability of the heart because of murmurs, or even functional disturbances, seeming to prove either aortic or mitral insufficiency or stenosis. Aneurism of the aorta is very seldom recovered from, but, besides a variable duration, whose period can almost never be anticipated with exactness, there appear to have been some cases of disappearance, or at least prolonged quiescence, of the tumor and of its morbid effects. Yellow atrophy of the liver is one of the disorders most rarely ending otherwise than in death. With a course altogether indefinite in time, there appears to be a tendency to exhaust vital energy, without self-limitation, in the different forms of organic degeneration, such as fatty heart, Addison's disease, chronic Bright's disease, diabetes mellitus, cirrhosis, and amyloid degeneration of the liver, etc. The same may be said also of the different forms of cerebral and spinal sclerosis, of pernicious anæmia, and of myxoedema. Lastly, it is an exception to a very general rule of fatality when a case of trichinosis, with well-marked abdominal, muscular, and general symptoms, ends otherwise than in death within a few weeks. Self-limitation is familiar in the natural history of typhus and typhoid fever, relapsing fever, yellow fever, cholera, diphtheria, whooping cough, mumps, small-pox, varicella, scarlet fever, and measles. In the sense of a definite duration of each paroxysm intermittent and remittent fevers are self-limited. Are they so also in tending toward recovery, without curative treatment within a certain time? This has been asserted, and in the case of remittent there is evidence that spontaneous cures do sometimes happen. Some observers aver that ague tends toward cessation of the chills after six, eight, or ten weeks. The obstinacy of the attacks in many instances under anti-periodic medication seems to make it probable that spontaneous recovery from intermittent hardly belongs to the typical natural history of the disease.