822 NUTRITION AND HEAT REGULATION. 



orated from the lungs and thus more heat is lost.* The distinc- 

 tion between the two great groups of animals is not entirely abso- 

 lute, but it is sufficiently marked to constitute a striking physio- 

 logical characteristic. 



The temperature of the human body is measured usually by 

 thermometers placed in the mouth, in the axilla, or in the rectum. 

 Measurements made in this way show that in general the tempera- 

 ture in the interior of the body (rectal) is slightly higher than on the 

 surface of the skin. The average temperature in the rectum is 37.2 

 C. (98.96 F.); in the axilla, 36.9 C. (98.45 F.); in the mouth, 

 36.87 C. (98.36 F.). We may speak of the body temperature, 

 therefore, in the places in which it can be conveniently measured, as 

 varying between 36.87 C. and 37.2 C. Some of the internal or- 

 gans have a higher temperature, particularly during their period of 

 greatest activity. The temperature of man, measured in the places 

 mentioned, shows also a distinct variation during the day, a diurnal 

 rhythm. This daily variation has been measured by many ob- 

 servers, and shows individual peculiarities that depend largely upon 

 the manner of living, time of meals, etc. In general it may be said 

 that the lowest temperature is shown early in the morning, 6 to 

 7 a.m. ; that it rises slowly during the day to reach its maximum 

 in the evening, 5 to 7 p.m. ; and falls again during the night. The 

 difference between early morning and late afternoon or evening 

 may amount to a degree or more centigrade, and this fact must be 

 borne in mind by physicians when observing the temperature of 

 patients. Muscular activity and food appear to be the factors that 

 are mainly responsible for the rise in temperature during the day. 

 Most observers state that when the habits of life are reversed for 

 some time that is, when work is performed and meals are eaten 

 during the night, and the day is given up to sleep and rest the daily 

 variation of temperature is inverted to correspond, that is, the 

 highest temperature is observed in the early morning and the lowest 

 in the late afternoon. Age also has a slight influence. Newly born 

 infants and young children have a somewhat higher temperature 

 than adults. The difference may amount to half a degree or 

 a degree centigrade, 37.6 C. in infants as compared with 

 36.6 C. or 37. 1 C. in the adult. It is known, also, that the heat- 

 regulating mechanism in infants and young children is not so 

 efficient as in adults, and that therefore febrile disturbances are more 

 easily excited in the former than in the latter. In the matter of body 

 temperature, as in so many other characteristics, aged people show 

 a tendency to revert to infantile conditions. Their temperature, 

 according to most observers, is slightly higher than in middle life. 



* See Langlois, " Journal de physiologie et de pathol. generate, " 1902, 

 249. 



