1308 PHYSIOLOGY 



animal liable to have his activities reduced and paralysed by a sudden 

 spell of cold weather ; this greater independence of the environment 

 which is characteristic of elevation of type, has been achieved by the 

 warm-blooded animals, including man. Such animals are often 

 spoken of as homoiothermic, i.e. animals possessing a uniform tempera- 

 ture, in contradistinction to the cold-blooded animals, which are 

 poikilothermic and possess a temperature varying with that of their 

 surroundings. 



Amongst the warm-blooded animals the body temperature may 

 be very different according to the species. In birds it is generally 

 from 39 to 40 0. ; in mammals it varies from 35 to 40 C. The 

 temperature of man varies within slight limits about 37C. (98-4 F.). 



THE DIURNAL VARIATIONS IN THE BODY TEMPERATURE 



In any animal the seat of heat production, e.g. a contracting 

 muscle, must be warmer than an inactive tissue, and this again than 

 a tissue from which heat is being rapidly abstracted, such as the skin. 

 Owing, however, to the rapidity of the circulation of the blood, the 

 temperature of the internal organs can be regarded as approximately 

 uniform. The temperature of man is usually taken in the mouth, 

 rectum, or axilla. In the case of the mouth the temperature is 

 liable to fluctuation with the rate of breathing, the mouth being cooled 

 by the passage of the air through the nasal cavities. There is also 

 probably loss of heat through the cheeks. In order to determine the 

 temperature in this situation the mouth should be kept closed for a 

 few minutes and then the bulb of the thermometer inserted under the 

 tongue, and the lips kept closed on the stem of the thermometer for 

 five minutes. Except in cases where the cutaneous vessels are much 

 dilated, the temperature of a thermometer in the axilla takes a con- 

 siderable time to rise to that of a thermometer in the mouth ; it 

 should never be left less than ten minutes in this situation. The follow- 

 ing Table represents the temperature of different parts of the body : 



SURFACE 



Skin covered with clothes 33 to 35 C. 



Naked skin in bath at 5 C 17 C. 



25 C 26-5 C. 



MUSCLES 12 MM. BELOW THE SURFACE 



In bath at 5 C 36-3 C. 



25 C. . 36-9 C. 



The body temperature of man shows variations of several tenths of 

 a degree according to the time of day at which the temperature is 

 taken. The highest temperature is obtained about six or seven in 

 the evening, and the lowest at about four or five o'clock in the morning. 



