of impending evil, hurried and shallow breathing, disturbance about the heart, gasping, giddiness, headache, occasionally nausea or vomiting, thirst, anorexia (want of appetite), feverishness, which soon amounts to fervent heat of skin; the surface may be dry or moist, the pulse varies; and these conditions gradually become aggravated and frequently are worse at night, when the patient passes into a state of unconsciousness and dies.
The symptoms point to a profoundly disturbed state of the cerebrospinal nerve-centers, and to pathological changes in the organs whose functions have been so greatly disturbed.
Death is caused by asphyxia and apnœa, and in some cases probably by cerebral hæmorrhage. Recovery is often incomplete, resulting in permanent impairment of health, and generally in intolerance of heat and of exposure to the sun. These morbid conditions being due to heat alone, are liable to occur whenever there is exposure to a high temperature, whether solar or artificial. Soldiers marching or fighting, when oppressed by weight of clothing or accoutrements, are apt to suffer either from simple heat-exhaustion or from that form of insolation which results from direct action of a powerful sun on the head and spine. Soldiers, laborers, artificers, and people in factories, heated rooms, hospitals, barracks, tents, and even ships, may suffer from heat-exhaustion, which may pass into the same dangerous condition of heat-asphyxia. People in the hay-field, or otherwise exposed to great heat, especially if they have indulged in excess of alcoholic stimulants and food, may suffer. Weak persons with defective hearts may die in this state of syncope. Soldiers or others, when exposed to great heat, may drop out of the ranks, fall in a state of syncope and die on the spot, or pass into a state of coma and die later; or they may recover, after being in great danger, with damaged nerve-centers, and are rendered quite unfit for further service, or even residence in a hot climate. These cases occur on exposure to the direct action of the sun's rays when the atmospheric temperature is also high, and especially when unusual exertion is made, or when the individual is depressed by previous illness or the exhaustion due to dissipation, intemperance, or even undue indulgence in stimulants.
But the most serious cases are those that come on under cover by night as well as by day, and apart from the direct solar rays. Heat alone, especially when the atmosphere is loaded with moisture so as to prevent evaporation from the person, is the real cause of the disease.
Vigorous, healthy persons of moderately spare frame, with sound viscera, and who are of temperate habits, if the atmosphere be pure and moderately dry, can sustain a great amount of heat. Acclimatization has also some influence in conferring toleration. Fresh arrivals in the tropics are more prone to suffer than those who have become accustomed to the climate, and have learned how to protect themselves. It is well known that a native can bear an amount of sun on
