SECTION XXIX 

 ANIMAL HEAT 



CHAPTER XCII 

 THE PRODUCTION AND DISSIPATION OF HEAT 



Thermometry and Calorimetry.— Inasmuch as all chemical proc- 

 esses require an optimum degree of temperature for their completion, 

 it raay be concluded that the assimilation and dissimilation of the 

 different foodstuffs cannot be effected in the absence of a definite 

 measure of heat. This heat may be derived from two sources, namely, 

 as radiating or bound energy from without, or as energy liberated in the 

 course of the different chemical changes to which the tissues and organs 

 of the body are subject. Under ordinary circumstances, the latter 

 form of heat is of by far the greatest functional importance to us, but 

 its detection and actual measurement presents many rather unexpected 

 difficulties, so that very sensitive instruments must be employed in 

 order to prove its liberation. In the case of such structures as the 

 muscles and glands, we make use of the so-called thermo-electric ele- 

 ments which consist of two dissimilar metals, such as German silver 

 and iron, soldered together. One of these is placed in some indifferent; 

 tissue or in the blood-stream, while the other is inserted in the organ, 

 the temperature of which is to be determined. If the binding posts 

 of these two pairs of elements are then connected with a galvanometer, 

 it will be found that the least production of heat at the point of solder- 

 ing gives rise to a difference in potential which will be accurately in- 

 dicated by the deflection of the galvanometric needle. 



It is evident, however, that this method cannot be employed to 

 determine the total heat-production of an animal nor its body-tempera- 

 ture, because this method must necessarily remain restricted to single 

 and separate organs. Should we desire to determine the temperature 

 prevailing within the body of an animal we must, of course, make use of 

 a thermometer which is inserted in any one of its cavities or recesses 

 and is allowed to remain there until the mercurial indicator has as- 

 sumed a stationary position.^ It must be evident, however, that 

 thermometry merely serves as a means of determining the tempera- 

 ture existing at any particular moment and cannot yield data regarding 

 the total amount of heat produced by the animal. Should we wish to 



* The thermometer was devised by Galilei in 1603. The first thermometric 

 determinations upon man were made by Sanctorius in 1626. 

 fifl • 1089 



