VI. CALORI METRIC MEASUREMENTS 183 



ing of animals best fit for given climatic conditions. Attempts are 

 underway to combine the high rate of production and efficiency of food 

 utilization for meat and milk inherent in our modern western breeds 

 of cattle wdth the great ability to endure high environmental tempera- 

 tures, which characterizes Indian breeds (Brahman cattle) . A stand- 

 ard scale for measuring thermostatic ability would undoubtedly be ad- 

 vantageous for this breeding work. 



2. IMeasiirenieiil of Radiant Energy 



Radiant energy is often measured by transforming it into heat 

 (12). The transformation takes place as a rule in a so-called black 

 body, and the heating effect is measured either by rotation of a paddle 

 wheel, as in Crooke's radiometer, by the change in temperature of the 

 arm of a Wheatstone bridge, as in Langley's bolometer, or as a ther- 

 moelectric potential of a thermocouple, as in Boys' radiomicrometer 

 or in Hardy's radiometer for measuring radiation rates of human skin 

 (13). Measurements of radiant energy are basic in research on photo- 

 synthesis (14)- They are also important in the study of heat ex- 

 change of animals and man. 



3. Measurement of Chemical Energy 



The most widespread application of calorimetry in biological re- 

 search is the measurement of chemical energy. Among the innumer- 

 able possible aspects of life, the one that shows life as a transformation 

 of energy has proved to be particularly fruitful. In the great process : 

 radiant energy — > chemical energy -^ heat, the first step is of particu- 

 lar importance in plant physiology, the second in animal physiology. 



From the sun's great stream of radiant energy that flows down to 

 the level of heat, organisms channelize a streamlet and retard the deg- 

 radation process to heat, using this radiant energy for the synthesis 

 of organic compoimds. These compounds in turn furnish energy 

 necessary for the life of the allotrophic organisms, particularly ani- 

 mals. 



The efficiency of plant production may be expressed in terms of 

 calories of chemical energy yield per acre or per calorie of radiant 

 energy received on the ground. Food requirements and perform- 

 ances of work of man and animals are measured in calories, and im- 

 portant deductions in biochemistry are based on free energy (11,36). 



