ANIMAL HEAT. 585 



specific heat, and temperature of any substance the total quantity of heat stored 

 in it at a given temperature may be readily calculated. Thus, if the animal 

 experimented upon weigh 20 kilos, its specific heat be 0.8, and its temperature 

 be 39, the total quantity of heat stored would be 20 X 0.8 X 39 = 62.4 kilo- 

 gramdegrees. In calorimetric work the total heat in the organism is seldom 

 considered, but the specific heat of the organism is of importance in determin- 

 ing the quantity of heat involved in a change of the animal's temperature. For 

 instance, should the animal weigh 20 kilograms and its temperature be increased 

 or decreased 0.2, the quantity of heat added to or taken from the heat of the 

 body, as the case may be, would be 20 X 0.8 X 0.2 = 3.20 kilogramdegrees. 

 These calculations are of fundamental importance in studying heat-production 

 and heat-dissipation. 



In making estimates of the dissipation of heat no regard is paid usually to 

 the quantity lost in the urine and feces, because the error involved is so slight, 

 but the quantities imparted to the air, both in warming the inspired air and in 

 evaporating water from the lungs and skin, represent important percentages. 



Calorimetry is spoken of as direct and indirect. The former method is 

 the direct determination of the amount of heat produced and dissipated ; the 

 latter is the indirect determination based upon estimates of the quantities of O 

 absorbed and CO 2 eliminated, or upon the amount of potential energy ingested 

 in the food and probably transformed into kinetic energy within the body 

 (p. 582). 



Calorimeters of various forms have been employed, some of which have 

 been devised to study the body as a whole, while others are adapted only for 

 studying parts, such as a leg or arm. They may be classified as ice, air, and 

 water calorimeters in accordance with the chief medium employed to absorb 

 the heat. They consist essentially of an insulated jacket of ice, air, or water, 

 which encloses the animal and serves to absorb the heat. The ice calorimeter 

 is impracticable for physiological uses because the animal is placed under 

 such abnormal temperature conditions ; the air calorimeter has many inherent 

 defects, and until very recent years has found but little acceptance ; the water 

 calorimeter is the form of apparatus usually employed, having been first used 

 by Crawford in 1788; it has been materially modified by Despretz and 

 Dulong and subsequent investigators. The now classical instrument of 

 Dulong consists of two concentric cases. The animal is placed within the 

 smaller case, which is submerged in the water contained in the larger case, 

 this in turn being placed within a large box, between which and the calorime- 

 ter some non-conducting material such as feathers or wool is packed. Suit- 

 able openings are made for the proper supply of fresh air and for the agitation 

 of the water in the calorimeter so that an equalization of the temperature of 

 the instrument can be obtained. This apparatus has certain serious defects, 

 however, which render it troublesome for expeditious and accurate work. An 

 improved form devised by the author 1 which is now in general use meets 

 every essential requirement for a satisfactory instrument. The apparatus con- 



1 Reichert: University Medical Magazine, 1890, vol. 2, p. 173. 



