ANIMAL HEAT. 



433 



The total Calories obtained from other diet scales would be as follows: 

 Ranke's, 2335; Volt's, 3387; Moleschott's, 2984; Atwater's, 3331; Hultgren's, 

 3436. These numbers indicate theoretically the total heat-production in 

 the body daily. 



2. Calorimetric Measurements. By this method the heat dissipated 

 from the body of an animal is directly collected and measured, and the 

 amount so obtained is taken as a measure of the heat evolved by the oxidation 

 of the food. A calorimeter is therefore an apparatus for the direct estimation 

 of the quantity of heat dissipated from the body in given time. The sub- 

 stance employed for collecting and measuring the heat is either water or 

 air. The calorimeters in general use consist essentially of twojjmetallic 

 boxes placed one within the other, though separated by a space sufficiently 

 large to hold a definite amount of water (Fig. 203). The animal is placed 

 in the inner box, which is also provided with tubes for the entrance of fresh 

 and the exit of expired air. The heat radiated is absorbed by the water and 

 its temperature raised. To 

 prevent loss by radiation 

 and to render it independ- 

 ent of changes in the 

 surrounding temperature 

 the calorimeter is sur- 

 rounded by a poorly con- 

 ducting material, such as 

 wool. The temperature of 

 the animal is taken at the 

 beginning and the end of 

 the experiment. If the tem- 

 perature of the animal re- 

 mains the same at the end 

 of the experiment, then the 

 heat absorbed by the water 

 represents the amount pro- 

 duced by the animal. If, 

 on the contrary, the tem- 

 perature of the animal rises 



FIG. 203. WATER CALORIMETER or DULONG. D 

 and D'. Tubes for the entrance and exit of air. T and T'. 

 Thermometers for ascertaining the temperature of the 

 water. S. A mechanic contrivance for stirring the water 

 for the purpose of distributing the absorbed heat uni- 

 formly. To prevent the escape of heat with the expired 

 air, the tube D' is wound many times in the water-space 

 beneath the animal cage. 



or falls, the number of calories so retained or lost must be added to or sub- 

 tracted from the amount absorbed by the calorimeter. In the determination 

 of the absolute amount of heat retained or lost by the animal above or 

 below the initial temperature, as well as that absorbed by the materials of 

 the apparatus in these various instances, the water equivalent of the tissues 

 of the animal and the materials of the calorimeter must be obtained, and 

 then added to or subtracted from, as the case may be, the amount of water 

 in the calorimeter, and the amount thus obtained multiplied by its rise in 

 temperature. In properly conducted experiments in which the sources 

 of error are reduced to a minimum there is a very close correspondence 

 between the total physiologic heat value of the food and the amount col- 

 lected by the calorimeter. Thus, in an experiment detailed by Rubner, a 

 dog was given during twelve days 228.06 grams of protein and 340.4 grams 

 of fat, the physical heat value of which was estimated at 4419 Calories. .^The 

 28 



