Insolatioyi. Stui-stroke. Thermic Fcve7\ 41 



A large proportion of cases in the human subject are attacked 

 during the night, and again at sea where an attack in a passenger 

 is practically unknown, it is terriljly common among stokers 

 working in a close atmosphere of 100° to 150° F. 



The attendant conditions have much influence in determining 

 an attack, thus it is generally held that heat with excess of moist- 

 ure is the most injurious, yet in Cincinnati, statistics showed a 

 greater number of cases in man when the air was dry. The sup- 

 pression of perspiration and the arrest of cooling by evaporation 

 in the latter case would tend to a rapid increase of the body tem- 

 perature, and the condition would be aggravated by the electric 

 tension usually present with the dry air. With the hot, moist air 

 perspiration might continue, but evaporation would be hindered, 

 and there would be arrest of the cooling process and an extreme 

 relaxation of the system. 



Again, it is usually found that seizures take place during or 

 after hard muscular exertion in a hot period, and much importance 

 is attached to tlie attendant exhaustion, the excess of muscular 

 waste, and the alteration of the myosin, which latter coagulates 

 at a lower temperature in the over- wc-rked animal. But on the 

 other hand, experiment shows that the animal confined to abso- 

 lute inactivity in the hot sunshine or in a high temperature (at 

 go°), dies in a few hours, whereas another animal left at liberty 

 in the same temperature does not suffer materially. The explana- 

 tion appears to be that the dog, kept absolutely still , has the contiu- 

 iious action of the heat on the same parts and on the same blood, 

 for the capillaries dilate, and the blood is delayed, overheated, 

 and surcharged with carbon dioxide, and the result is either syn- 

 cope from heart failure, or asphyxia from excessive carbonization 

 of the blood. Back of these and concurring with them is the par- 

 alysis of the va.so-motor and heat generating nerve centres, from 

 the high temperature or the condition of the blood. 



The excessive carbonization of the blood deserves another word. 

 The prolonged contact of the blood and air in the lungs is essen- 

 tial to the free interchange of oxygen and carbon dioxide. Vie- 

 rordt showed that with sixty respirations per minute the expired 

 air became charged with but 2.4 per cent, of this gas, whereas 

 with fourteen respirations it contained 4.34 per cent. Therefore, 

 with violent muscular work (which charges the blood with carbon 



