PHYSICAL SOURCES OF HEAT. 425 



(/3) When a neutral salt is changed into a basic one (Andrews). In the blood, the 

 sulphuric and phosphoric acids derived from the combustion of S and P are united 

 with the alkalies of the blood to form basic salts. The decomposition of the car- 

 bonates of the blood by lactic and phosphoric acids forms a double source of heat, 

 on the one hand, by the formation of a new salt, as well as by the liberation 

 of C0 2 , which is partly absorbed by the blood. 



(7) The combination of haemoglobin with ( 36). 



In connection with those chemical processes, whereby the heat of 

 the body is produced, heat-absorbing intermediate compounds are 

 not unfrequently formed. Thus, in order that the final stage of more 

 complete saturation of the affinities be reached, intermediary atomic 

 groups are formed, whereby heat is absorbed. Heat is also absorbed 

 when the solid aggregate condition is dissolved during retrogressive 

 processes. But these intermediary processes whereby heat is lost, are 

 very small, compared with the amount of heat liberated when the 

 end-products are formed. 



(2.) Certain physical processes are a second source of heat. 



(a) The transformation of the kinetic mechanical energy of internal 

 organs, when the work done is not transferred outside the body, pro- 

 duces heat. Thus the whole of the kinetic energy of the heart is 

 changed into heat, owing to the obstructions which are opposed to the 

 blood-stream. The same is true of the mechanical energy evolved by 

 many muscular viscera. The torsion of the costal cartilages, the friction 

 of the current of air in the respiratory organs, and the ingesta in 

 the digestive tract, all yield heat. 



An excessively minute amount of the mechanical energy of the heart is trans- 

 ferred to surrounding bodies by the cardiac impulse and the superficial pulse-beats, 

 but this is infinitesimally small. During respiration, when the respiratory gases 

 and other substances are expired, a very small amount of energy disappears 

 externally, which does not become changed into heat. If we assume that the daily 

 work of the circulation exceeds 86,000 kilogram-metres, the heat evolved is equal to 

 204,000 calories, in 24 hours ( 93), which is sufficient to raise the temperature of a 

 person of medium size, 2C. In former times, Boerhave and others thought that 

 the heat of the body was chiefly due to the friction of the blood within the 



(b) When, owing to muscular activity, the body produces work which 

 is transferred to external objects, e.g., when a man ascends a tower or 

 mountain, or throws a heavy weight, a portion of the kinetic energy 

 passes into heat, owing to friction of the muscles, tendons, and the 

 articular surfaces, as well as to the shock and pressure of the ends of 

 the bones against each other. 



(c) The electrical currents which occur in muscles, nerves, and glands, 

 very probably are changed into heat. The chemical processes which 

 produce heat evolve electricity, which is also changed into heat. This 

 source of heat, however, is very small. 



