b 



THE PRODUCTION AND DISSIPATION OF HEAT 1095 



higher than that of the external jugular vein. Very similar differences 

 are displayed by the blood of the portal vein before and after meals, 

 as well as by the blood of the vein draining a muscle when the latter 

 is either allowed to rest or is made to contract. Even the mere 

 raising of the arm above the head suffices to lower the temperature 

 of the hand 0.2° C. 



The average temperature of the blood traversing internal channels, 

 is 39° to 40° C, while that of the exposed parts may be only 28° to 

 35° C. KunkeP gives the following values: Forehead 34.1° C, cheeks 

 34.4° C, tip of ear 28.8° C, sternum 34.4° C, and thigh 34.2° C. In 

 man, the body-temperature is measured as a rule by placing the ther- 

 mometer below the tongue, care being taken to keep the lips closed to 

 prevent its cooling by the respiratory currents of air. In adults, it 

 may also be measured in the axilla, and in children usually in the rec- 

 tum. While the time during which the thermometer should be left 

 in situ, varies with its sensitiveness, 2 to 3 minutes usually suffice 

 for its indicator to reach its highest' level. The average axillary tem- 

 perature is 36.9° C, the oral temperature 37.1° C, and the rectal 

 temperature 37.3° C. 



Factors Varying the Body-temperature.^ — ^While it is our custom 

 to adhere strictly to these average values, it should be remembered 

 that certain minor fluctuations are not at all uncommon. In other 

 words, even the homoiothermal animals frequently show variations in 

 their temperature which are brought about by such factors as age, sex, 

 time of day, meals, exercise, season, climate and clothing. While 

 these deviations rarely amount to more than a degree or two and are 

 temporary in their nature, certain conditions may also arise at times 

 which produce a much more intense and lasting difference. Quite 

 aside from the ordinary febrile reactions, the outside temperature may 

 be raised in such a measure, that, owing to a diminished loss of heat, 

 the body-temperature quickly mounts to 40° C. and over. This change 

 is usually associated with the symptoms characterizing fever and heat- 

 stroke, i.e., with an increase in the frequency of the heart and respira- 

 tion (heat-polypnea), fatigue, headache and loss of consciousness. 

 When the rectal temperature rises to 44° C, death visually results 

 within a very short time. 



Hot moist air is far more oppressive and dangerous than hot dry 

 air, owing to the inability of the body to rid itseh of the superfluous 

 heat by sweating. In other words, in the former instance ordinary 

 radiation cannot be augmented so well by a loss of heat in the form of 

 bound heat'. In this regard, the cold-blooded terrestrial animals have 

 the advantage, because they are able to burrow underground or to 

 dive under water to increase their evaporation. Very similar condi- 

 tions exist in the plants, because any rise in the external temperature 

 increases their transpiration, thereby lowering their own temperature 

 much below that of the atmosphere. This protects them against dry- 

 1 Kunkel, Zeitschr. fiir Biol., xxv, 1889, 69. 



