i66 Teuipcrafurc Disturbances. 



38°— 40° C; dog, 37-5"— 39° C.; cat, 38°— 39° C. ; birds, 

 4i.5°-42.5° C. 



The warm blooded animal maintains the constant physiological 

 level of temperature by the continued operation of the heat dis- 

 sipating powers ; if there were no such loss, the amount of heat 

 production would be sufficient to cause an increment of about one 

 degree centigrade in the temperature of the blood every half hour. 



Passive Hyperthermia. By limitation of heat dissipation 

 the body may become overheated, particularly when the cause 

 is some external physical influence which hinders heat loss by 

 evaporation. Although in a dry atmosphere where there is no 

 restriction to evaporation the body is capable of enduring even high 

 temperatures of the surrounding air, the body heat increases rap- 

 idly in a hot, moist atmosphere, heat loss by evaporation being 

 impossible, and all the more if in addition there be increased pro- 

 duction from muscular exercise. In a warm bath of 40° — 41° C. 

 the human body temperature may even in half an hour reach 40° C. ; 

 in water of 37° C, it rises about 1° C. in an hour, and in an hour 

 and a half about 2° C. 



Animals closely packed in hot railway cars experience consid- 

 erable increase of temperature ; in warm, damp air animals closely 

 herded in long drives (droves of hogs, oxen yoked to wagons) may 

 have their temperature reach more than 40° C. Under such cir- 

 cumstances where only external physical conditions render the 

 regulation of the body temperature impossible or where (perhaps 

 coincidently) unusual accession of heat production occurs because 

 of exceptional muscular exercise, there is really no true febrile tem- 

 perature present, but rather only a passive heat accumulation, 

 passive hyperthermia; the mechanism of heat dissipation is acting 

 in its fullest capacity and is insufficient only because the demands 

 upon it are excessive (Krehl). Thermolysis so far as the animal 

 body is concerned is not at fault ; but fails because of conditions 

 existing in the external surroundings. 



Whether pathological results follow such passive hyperthermia 

 will depend upon the persistence of the condition and the subject's 

 power of adaptation. Men and animals living in tropical coun- 

 tries give evidence upon this last point ; and, too, it is commonly 

 seen that when a number of individuals are subjected to excessive 

 temperatures there are only certain ones who suffer pathologically, 

 those probably whose thermo-regulatory mechanism is of inferior 

 efficiency. Passive hyperthermia may reach 42° — 45° C, and may 



