3l8 HOMOIOTHERMAL AND POIKILOTHERMAL ANIMALS. 



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 trans- 

 formation of the kinetic mechanical energy of internal organs, when the work 

 done is not transferred outside the body, produces heat. Thus the whole of the 

 kinetic energy of the heart is changed into heat, owing to the resistance opposed to 

 the blood-stream ( 93). 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 transferred to 

 surrounding bodies by the cardiac impulse and the superficial pulse-beats, but this is innni- 

 tesimally small. During respiration, when the respiratory gases and other substauces 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 twenty-four hours ( 93), which is sufficient to 

 raise the temperature of a person of medium size 2 C. 



(h) When, owing to muscular activity, the body produces work which is trans- 

 ferred 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. 



(d) Other processes are the formation of heat from the absolution of C0 9t by the concentration 

 of water as it passes through membranes, in imbibition, and tlic formation of the solids, e.g., of 

 chalk in the bones. After death, and in some pathological processes during life, the coagula- 

 tion of blood and the production of rigor mortis are sources of heat. 



207. HOMOIOTHERMAL AND POIKILOTHERMAL ANIMALS. In 



place of the old classification of animals into " cold-blooded " and " warm-blooded," 

 another basis of classification seems desirable, viz., the relation of the temperature 

 of the body to the temperature of the surrounding medium. Bergmann introduced 

 the word homoiothermal for the warm-blooded animals (mammals and birds), 

 because these animals can maintain a. very uniform temperature, even although the 

 surrounding temperature be subject to considerable variations. The so-called cold- 

 blooded animals are called poikilothermal, because the temperature of their 

 bodies rises or falls, within wide limits, with the heat of the surrounding medium. 



When homoiothermal animals are kept for a long time in a cold medium, their 

 heat-production is increased, and when they are kept for a long time in a warm 

 medium it is diminished. 



Fordyce gave a proof of the nearly uniform temperature in man. A man remained ten 

 minutes in an oven containing very dry hot air ( 218), and yet the temperature of the palm 

 of his hand, mouth, and urine was increased only a few tenths of a degree. Becquerel and 

 Brechet investigated the temperature of the human biceps (by means of thermo-electric 

 needles), when the arm had been one hour in iced water, and yet the temperature of the 

 iniisi ular tissue was cooled only 0'2" C. The same muscle did not undergo any increase in 

 temperature, or at most 0*2 C, when the man's arm was placed for a quarter of an hour in 

 water at 42 C. 



If heat be rapidly abstracted (^ 225) or rapidly supplied ( 221) to the body, 

 so as to produce rapid variation of the temperature, life is endangered. 



