368 HUMAN PHYSIOLOGY 



panting from long exertion may show an elevation of 

 the rectal temperature but no corresponding rise in the 

 mouth. 



There is a slight daily rise and fall of the temperature 

 wherever measured. The lowest point is passed in 

 the early morning before the reluctant muscles have 

 been roused to much activity. There is an upward 

 tendency through the day and the highest level is reached 

 late in the afternoon or early in the evening. The 

 extent of the fluctuation is rather more than 1F. When 

 there is fever the same ascending curve is usually re- 

 corded and the patient is likely to be more restless and 

 uncomfortable toward night. 



While we recognize the daily variation it is still plain 

 that the approximate constancy of the body tempera- 

 ture is the outstanding fact. Where heat-production is 

 always going on uniformity of temperature must be 

 due to a balance between this production and the con- 

 current loss, between thermogenesis and thermotaxis, if 

 we adopt the language of science. The place and 

 manner of heat-production are already familiar; it occurs 

 chiefly in the skeletal muscles with supplementary con- 

 tributions from the heart and the glands. We have 

 now to add some details regarding heat loss. 



The total for the day is that of the metabolism; we 

 will again assume 2500 Calories. We know that some 

 of this heat is imparted to the air and the surroundings 

 in general. Another fraction of it becomes latent 

 through the evaporation of water. The relative amount 

 of the two portions will depend on the external tem- 

 perature. If this is low, as in winter, the subject will 

 evaporate much less water than if it is high. A water 

 loss from the breathing passages and the skin aggre- 

 gating 1000 grams will render latent over 500 Calories, 

 as previously stated. The remaining Calories of our 

 assumed total about 2000 will, in this case, be directly 

 measurable as heat given to the surroundings. 



A proportion like that just suggested may be ex- 



