or from a highly-heated atmosphere, or indeed from some artificial source.
But while heat is rightly regarded as the principal if not the sole exciting cause, there are other conditions, as previously stated, which contribute largely toward bringing on the attack. Of these, overcrowding, and its associate, insufficient ventilation, are among the most important. The histories of the outbreaks that have occurred in barracks, in tents, and on shipboard, refer to these conditions as always present, and also mention that both officers and men in every other way similarly circumstanced, but provided with plenty of room and ventilation, did not suffer.
Another and equally important predisposing cause is the exhaustion produced by prolonged exertion. The fact that a large proportion of the cases occurring in this country are of persons engaged in laborious occupations is evidence of this, and if more is needed it is found in the experience of army-surgeons in India, who state that some of the severest epidemics ever witnessed in that country took place among the troops toward the close of long and fatiguing marches, when not a case was observed while the men were fresh and vigorous.
Want of acclimatization is set down as another powerful predisposing cause. "Foreigners," says Dr. Wood, "are always attacked in much larger numbers than natives of the tropics. It must be remembered, however, that no amount of acclimatization will afford certain protection, as even the Hindoo, born and bred in the stifling air of Bengal, is occasionally attacked.
Tight-fitting clothing, which impedes the circulation and hinders the movements of the body, likewise invites attack. Formerly soldiers in India were dressed, in the hottest weather, with tightly-buttoned coats, stiff leather stocks, heavy cross-belts over the chest, and a cap peculiarly adapted to concentrate the rays of the sun upon the head. When so accoutred, according to the testimony of their medical officers, sunstroke among them was common; and, since this style of dress has been done away with, it is much less frequent.
Persons addicted to spirit-drinking are by many writers believed to furnish a much larger proportion of cases than abstainers.
The presence of a large amount of watery vapor in the air is held, by Parkes and others, to predispose to sunstroke. By opposing evaporation from the surface, it favors the rise of animal temperature.
Other causes predisposing to sunstroke are given by different writers; they are, however, of the same general nature as those already enumerated, being simply conditions which either diminish the powers of the system, or for the time being impose upon them some heavy tax. Whether death from sunstroke is due to the action of heat on the nervous system, or to the coagulation of the muscle-plasma (myosin) of the heart, or to blood-poisoning, or in some cases to one, and in others to another of these causes, as maintained by dif-
