THE HEAT OF THE BODY. 479 



tact with external bodies, usually colder than itself, is cooler 

 than the internal organs; its temperature in health is from 

 36 to 37 C. (96.8-98.5 F.), being warmer in more protected 

 parts, as the hollow of the armpit. In internal organs, as 

 the liver and brain, the temperature is higher; about 43 C. 

 (107 F.) in health. In the lungs there is a certain quantity 

 of heat liberated when oxygen combines with haemoglobin, but 

 this is more than counterbalanced by loss of the heat carried 

 out by the expired air and that used up in evaporating the 

 water carried out in the breath, so the blood returned to the 

 heart by the pulmonary veins is slightly colder than that 

 carried from the right side of the heart to the lungs. 



The Sources of Animal Heat. Apart from heat received 

 from its surroundings in hot food and drink the sources of 

 heat in the Body are twofold direct and indirect. Heat is 

 directly produced wherever oxidation is taking place; and, 

 since almost invariably the chemically degrading or katabolic 

 processes going on in a living organ exceed the anabolic, the 

 living tissues at rest produce heat as one result of the chemical 

 changes supplying them with energy for the maintenance of 

 their vitality: and whenever an organ is active and its chemi- 

 cal metamorphoses are increased it becomes hotter: a secret- 

 ing gland or a contracting muscle is warmer than a resting 

 one, and the venous blood leaving noticeably warmer than 

 the arterial supplied to it. Indirectly, heat is developed 

 within the Body by the transformation of other forms of en- 

 ergy: mainly mechanical work, but also of electricity. All 

 movements of parts of the Body which do not move it in 

 space or move external objects, are transformed into heat 

 within it; arid the energy they represent is lost in that form. 

 Every cardiac contraction sets the blood in movement, and 

 this motion is for the most part turned into heat within the 

 Body by friction within the blood-vessels. The same trans- 

 formation of energy occurs with respect to the movements of 

 the alimentary canal, except in so far as they expel matters 

 from the Body; and every muscle in contracting has part of 

 the mechanical energy expended by it turned into heat by 

 friction against neighboring parts. Similarly the movements 

 of cilia and of amoeboid cells are for the most part converted 

 in the Body into heat. The muscles and nerves are also the 

 seats of manifestations of electricity, which, though small in 

 amount, for the most part do not leave the Body in that form 

 tout are first converted into heat. 



