THE MORBID EFFECTS OF HEAT. 501 



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, overcrowd- 

 ing, and its associate, insufficient ventilation, are among the most impor- 

 tant. 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 simi- 

 larly circumstanced, but provided with plenty of room and ventilation, 

 did not suffer. 



Another and equally important predisposing cause is the exhaus- 

 tion produced by prolonged exertion. The fact that a large propor- 

 tion 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 predispos- 

 ing cause. " Foreigners," says Dr. Wood, " are always attacked in 

 much larger numbers than natives of the tropics. It must be remem- 

 bered, 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 evap- 

 oration 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- 



