494 A TEXTBOOK OF PHYSIOLOGY 



reverses or tends to reverse this curve. In nocturnal birds the tem- 

 perature rises during the night, and falls during the day. On 

 travelling from Australia the curve adjusts itself as night becomes 

 day. The clergyman, the navvy, and the sailor, show temperature 

 curves which vary with the occupations and mode of life of each. 



A man resting in bed shows the same variation, but not to so 

 marked an extent. The diurnal variation is accounted for by the 

 " restlessness " during the day as compared with the deep rest of 

 sleep during the early night hours. It is more difficult to get absolute 

 rest in the light and noise of daytime. Infants, in the first few weeks 

 of life, show no marked variation. 



The taking of food, especially if it be warm or involve much work 

 on the part of the glands and muscles cf mastication, may raise the 

 general temperature of the body slightly. It plays no part, however, 

 in the production of the daily variation, which is approximately the 

 same whether a man be taking food or starving. 



Muscular activity raises the body temperature. After a three- 

 mile race the rectal temperature in a man not in good training was 

 as high as 105 F., and did not reach normal again until the sixth 

 hour after the race. After a strenuous game of football, rectal tem- 

 peratures of 102 to 103 F. are the rule. This is owing to the large 

 amount of heat .liberated by the muscles during muscular work 

 (see p. 552). 



If the subject be unsuitably clothed, and do hard muscular work 

 in a warm, windless atmosphere, there may result " heat-stroke." 

 Such a danger arises in the marches of soldiers in close formation on 

 warm, windless days. This is because the loss of heat from the body 

 cannot, under these conditions, keep pace with the heat production. 

 The subject, owing to his clothing and the high external temperature, 

 cannot lose heat rapidly enough by convection and sweating. The 

 clothes entangle air. and keep it stationary. This air is warmed 

 and moistened by the skin, and thus the body is enclosed in a layer 

 of stagnant humid air. In a crowd, too, the air is confined between 

 the bodies of the people. Wind sweeps the stagnant air out of the 

 clothes, and by throwing off the coat and opening the shirt we gain 

 relief. The clothing should be adapted to the requirements of climate 

 and occupation, not to fashion. 



The highest temperature recorded with recovery is in a case of 

 malaria (45 C.) or 113 F. ; the lowest temperature with recovery, 

 22-5 C. It ha been shown that rabbits lowered to 31 to 34 C. 

 breathed more slowly, and could not raise their temperature by 

 shivering. At 26 to 29 C. their nervous co-ordination was damaged, 

 and they were easily hypnotized. At 26 to 22 C. the arterial pressure 

 began to fall ; stimulation of the skin provoked twitches. At 19 C. 

 the vital centres became paralyzed, and death ensued. The tempera; 

 ture in local peripheral parts may be lowered far more, and these 

 parts recover from the temporary " numbness." Prolonged and 

 excessive cold leads to local death and gangrene (frost-bite). 



Generally speaking, the internal temperature of birds is warm 





