ANIMALS WITH CONSTANT AND VARIABLE TEMPERATURE. 381 



Thus, all of the kinetic energy of the heart is transformed into heat 

 through the resistance opposed to the blood-stream. The same may be 

 said of the kinetic energy of certain muscular viscera. Thus, the 

 torsion of the costal cartilages and the friction of the current of air 

 in the respiratory organs and of the contents of the digestive tract yield 

 a certain amount of heat. 



Small amounts of the mechanical energy of the heart are transmitted through 

 the apex-beat and the superficial pulse to surrounding parts, but these are ex- 

 ceedingly small. Also, in the respiratory movement, in the expulsion of the 

 respiratory gases, the expectorated and other matters, a small amount of energy 

 is conveyed to the outside, which is not converted into heat. Joule has 

 attempted to determine the amount of heat generated in consequence of the 

 kinetic energy lost by a flowing fluid. According to him the amount of heat 

 produced in this way as a result of the friction must stand in a relation to the 

 product of the difference between the initial and the terminal pressure in the 

 weight of the flowing fluid mass. If it be assumed that the daily work of the 

 circulation equals more than 86,000 meter-kilograms, it will be seen that the 

 resulting amount of heat in 23 hours will be about 204,000 calories, which is suffi- 

 cient to raise the temperature of the body of a medium-sized person about 2 C. 



(6) If the body through muscular activity does work transmitted to 

 the outside, as, for instance, if an individual throws a heavy weight or 

 ascends a tower, a portion of the kinetic energy is converted into heat 

 through the friction of the muscles, the tendons, the articular surfaces, 

 further through concussion and pressure of the ends of the bone upon 

 one another. 



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

 apart from the small amounts that pass outside of the body with suitable 

 conduction, are most probably transformed into heat. Thermogenic 

 chemical processes also generate electricity, which likewise is trans- 

 formed into heat. This source of heat is, however, quite insignificant. 



(d) As a further slight source of heat from physical causes there should yet 

 be mentioned heat-production through absorption of carbon dioxid, through the 

 condensation of water in its passage through membranes, and in the process of 

 imbibition, the formation of stable aggregate states, as, for instance, of cal- 

 cium in the bones. It is true, heat is again in part lost through the involution 

 of solid parts at advanced age. After death, at times also under pathological 

 conditions during life, coagulation of blood and the rigidity of muscles constitute 

 in this manner a source of heat. 



ANIMALS WITH CONSTANT AND WITH VARIABLE 

 TEMPERATURE. 



Instead of the older division of animals into cold-blooded and warm- 

 blooded (mammals and birds), it is advisable to base their classification 

 upon another characteristic, namely, the uniformity or the variability 

 of the bodily temperature with respect to external influences. For the 

 class of warm-blooded animals the name homoiothermic animals has been 

 introduced by Bergmann, because they are capable of maintaining their 

 bodily temperature with remarkable uniformity notwithstanding consid- 

 erable variations in the surrounding temperature. He designated cold- 

 blooded animals poikilothermic animals because their bodily temperature 

 rises and falls within wide limits in accordance with the temperature of 

 the surrounding medium. Accordingly, heat-production must be in- 

 creased in homoiothermic animals if exposed for a long time in a cold 

 atmosphere and diminished on exposure for a long time in a warm 

 atmosphere. 



