ANIMAL HEAT 159 



an animal may be measured by calculating the potential energy 

 from the food ingested or from the amounts of oxygen absorbed 

 and carbon dioxide given off. This is indirect calorimetry. 

 Direct calorimetry consists in measuring the heat directly by 

 means of a calorimeter. A calorimeter is an apparatus by 

 means of which the amount of heat given off by an animal 

 may be measured. It usually consists of two concentric cases 

 separated by ice, air, or water, and provided with thermometers 

 and gasometers so arranged as to insure proper ventilation 

 to the animal which is placed in the inner case. The object 

 of calorimetry is to determine the quantity of heat that is 

 dissipated in a definite time. A certain amount of the heat 

 is taken up by the apparatus, some is given to the air that 

 passes through the calorimeter, and finally some is lost in the 

 evaporation of water. 



To determine the amount imparted to the apparatus, it is 

 necessary before using to determine its calorimetric equivalent, 

 which is done by burning alcohol within it until the tempera- 

 ture has been raised 1 C. One gram of alcohol will yield about 

 7000 calories of heat, so that if 5 grams of alcohol are required 

 to raise the temperature of the calorimeter 1 C., then the 

 quantity of heat absorbed would be equal to 5 times 7000, 

 or 35,000 calories. This is the calorimetric equivalent. If an 

 animal has raised the temperature of the calorimeter 10 C., 

 the quantity of heat that it has given off would be equal to 

 10 times the calorimetric equivalent, or to 350 kilogram 

 degrees. The quantity of heat given to the air is determined 

 by measuring the amount of air passing through the calorim- 

 eter, and its temperature on its entrance and exit. The 

 volume of the air must be corrected for the increased tempera- 

 ture and then reduced to weight, after which it is multiplied 

 by the specific heat of air at C., and then by the number 

 of degrees of the increase of temperature. By specific heat 

 is meant the heat required to raise the temperature of any 

 substance 1 C., and is usually compared to water as a standard. 

 The specific heat of the animal body is about 0.8. The formula 

 for the correction of the volume of air is: 



v- v ' p 



760 (1 + 0.003665*) ' 



