CHAPTER II 



THE THERMIC ECONOMY OF THE ORGANISM 



SUMMARY. 1. Potential energy of foods from which the amount of heat 

 developed daily by the organism can be calculated. 2. Homoiothermic and 

 poikilothermic animals ; the thermic topography of man ; daily variations in 

 temperature. 3. Influence on the average temperature of age, sex, race, climate, 

 seasons, food, muscular activity, psychical activity. 4. Regulation of temperature 

 in homoiothermic animals and man ; internal conditions and the vasomotor system 

 which determine the equilibrium of temperature in an environment of moderate 

 warmth ; the nervous system as the regulator of the production of heat in order 

 to protect the organism from cold ; the nervous mechanisms regulating the loss 

 of heat by the evaporation of moisture from the lungs and skin, in order to protect 

 the organism from heat. 5. Experiments and clinical observations showing the 

 thermic effects of injuries to the spinal cord and brain. General theory of the 

 regulation of the exchange of material and energy by the nervous system. 

 Bibliography. 



THE exchange of material which we considered in the preceding 

 chapter is always accompanied by an exchange of energy, or, in 

 other words, a transformation of potential into actual energy or 

 the reverse. In the anabolic phases there is usually an accumula- 

 tion of energy, endothermic processes, in the catabolic phases a 

 development of energy, exothermic processes, the one being to 

 a certain extent the counterpart of the other. 



In all tissues or organs there is a continual development of 

 heat through oxidation ; the amount of heat developed during 

 these oxidising processes differs considerably according to the 

 nature and state of functional activity of the part. The heat 

 developed by the tissues or organs is imparted to the venous 

 blood flowing from them, which, circulating through the whole 

 organism, tends to diminish local differences of temperature. 

 The amount of heat developed in a given time by the organism 

 in a state of rest is equal to the total of the energy set free, that 

 is, of the potential energy which is transformed into actual 

 energy. During normal nutrition and equilibrium of the intake 

 and output this amount is about equal to the sum of the potential 

 energy introduced into the body with that portion of the food 

 which is to combine with the oxygen of the air absorbed by 

 means of external respiration. When the equilibrium of the 



51 



