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xxiv] Different writers mention a number of what may be described as minor symptoms. They vary in different cases, and are by no means always present or characteristic. Whether these minor symptoms are present or not, in siriasis the essential symptoms—high fever and profound nervous disturbance, generally associated with insensibility—are invariably in evidence.

Unless active measures to lower temperature are taken early in the progress of the case, and unless these measures are vigorously carried out, in the great majority of instances death will occur within a few hours, or even minutes, of the onset of insensibility. The immediate cause of death is generally the failure of respiration. Rarely do cases linger for a day or two. Partial recovery is sometimes followed by relapse. In favourable cases the disease usually terminates by crisis. Convalescence is rapid.

Mortality.—As might be supposed, some types of heat-stroke are much more dangerous than others; siriasis infinitely more so than ordinary heat-exhaustion. Treatment, if early instituted and judiciously carried out, has undoubtedly a powerful influence in reducing mortality. Taking one type of heat-stroke with another, the case mortality among English troops in India is about one in four; in the year 1892, of 223 European soldiers admitted to hospital for heat-stroke, 61 died.

Morbid anatomy.—A notable feature in fatal siriasis is the early appearance of rigor mortis. The blood is remarkably fluid, or but feebly clotted. The venous system is loaded, dark fluid blood pouring from the phenomenally engorged lungs and other viscera on section. Both blood and muscles are said to yield an acid reaction more or less pronounced. It has been stated that the red blood-corpuscles are crenated, and do not form rouleaux. If the post-mortem examination is made shortly after death and before decomposition changes have set in, the heart in early rigor mortis, particularly the left ventricle, will be found to be remarkably rigid; this rigidity is sometimes described as being of woodeny hardness.