960 NUTRITION AND HEAT REGULATION. 



Among physiological conditions that influence the body tempera- 

 ture, muscular work and meals, as stated above, have the most posi- 

 tive effect. Marked muscular activity implies a great increase in 

 the production of heat in the body and most observers find that 

 the initial result at least is a small rise in body temperature, a fact 

 which indicates that the heat regulation is not perfect; the excess 

 of heat produced is not dissipated promptly. This effect is natu- 

 rally most noticeable in tropical climates. In the period of rest 

 following upon work, on the contrary, the body temperature may 

 fall, owing probably to the fact that more heat is lost through the 

 flushed skin than is produced within the body. In this matter of 

 the effect of muscular work individual variations are to be expected, 

 since the perfection of the heat-regulating mechanisms may vary 

 somewhat in different persons. Meals also cause a slight rise in 

 body temperature, which reaches its maximum about an hour and 

 a half after the ingestion of the food. The explanation in this case 

 also is to be found doubtless in a greater production of heat, due to 

 the increased metabolism set up by the food (specific dynamic 

 action, see p. 914). The excessive production of heat is not 

 compensated completely by a corresponding increase in the 

 heat dissipated.* It is sufficiently obvious, perhaps, from these 

 facts that the temperature as measured by the thermometer is a 

 balance between the amount of heat produced and the amount of 

 heat lost or dissipated. The thermometer alone gives us no cer- 

 tain indication of the quantity of heat produced in the body. A 

 temperature higher than normal, fever temperature, may be due 

 either to an excessive production of heat or to a deficient dissipa- 

 tion. To understand and control the processes by which the body 

 temperature is kept normal it is necessary to discover a means for 

 ascertaining at any time the actual quantities of heat produced 

 and dissipated, and the effect upon each factor of different normal 

 and pathological conditions. The method used for determining 

 the quantity of heat is designated as calorimetry. It is necessary, 

 therefore, to describe the principle and construction of calorimeters 

 and the methods of calorimetry before attempting to explain the 

 mechanism of heat regulation. 



Calorimetry. A calorimeter is an instrument for measuring 

 the quantity of heat given off from a body. The unit employed in 

 these determinations is the calorie, that is, the amount of heat 

 necessary to raise 1 gm. of water 1 C.,or more accurately the amount 

 of heat required to raise 1 gm. of water from 15 to 16 C. This 

 unit is sometimes designated as a small calorie to distinguish it 

 from the large calorie (C), that is, the quantity of heat necessary 

 to raise 1 kgm. of water 1 C. The large calorie is equal to 1000 



* For further details see Richet, " La chaleur animale, " 1889 ; and Pem- 

 brey, "Animal Heat," Schaefer's "Text-book of Physiology," vol. i, 1898. 



