1092 



ANIMAL HEAT 



dioxid content by means of baryta water and of its aqueous vapor by 

 means of drying-tubes containing sulphuric acid. These values are 

 then compared with the data derived from analyses of the air entering 

 the calorimeter. These principles which have first been made use 

 of by Pettenkofer, are also embodied in the micro-calorimeter of Hill. 1 

 This apparatus which is especially adapted for the detection of very 

 small amounts of heat, consists of two thermos bottles in which the 

 loss of heat is prevented by exhausting the air from the space between 

 their outer walls. Each bottle is equipped with thermorelectric 

 elements which are connected in turn with a galvanometer. Both 

 are packed in sawdust. The organ to be experimented upon is then 

 placed in one of these bottles, while the other is filled with water as a 



RES PI FIAT I ON CHAMBER 

 used 



r~>Z U I - ' ' 



HiO N , . . . \ 

 COj o deficient ^ 



^S8L 



introduced. 



J C0z LJ HaP 

 absorbed by absorbed by 

 (No. OH j 



FIG. 529. DIAGRAM SHOWING CIRCULATION OF AIR THROUGH THE RESPIRATION CALORI- 

 METER. (Atwater and Benedict.) 



control. This apparatus is sensitized to detect one small calorie of 

 heat per gram of tissue during a period of 10 hours. 



Sources of Heat. Thennogenesis. While there is always a small 

 and variable amount of heat imparted to living beings from without, 

 their principal sourc^ of heat lies in the chemical processes evoked 

 within their different tissues and organs. Every contraction of mus- 

 cle, every act of secretion, and even every nervous reaction gives rise 

 to a small amount of heat, which together then form the total quantity 

 of heat evolved by the animal. These cellular oxidations consist 

 essentially of a union of oxygen with carbon and hydrogen to form 

 carbon dioxid and water. In last analysis, therefore, the body-heat is 

 derived from the food taken into the body. Other processes of dis- 

 integration, such as are effected by hydrolysis, also produce a certain 



1 Jour, of Physiol., xlv, 1918, 261, and ibid., xlvi, 1913, 81 ; also : Williams, Jour. 

 Biol. Chem., xii, 1912, 349. 



