182 MAX KLEIBER 



latent, not only as latent heat of melting or as heat absorbed in a 

 chemical change but also as mechanical work. 



Some agent remains constant in all these changes. I'his agent is 

 called energy. Work, light, electric potential, and, since Einstein, 

 also mass are various manifestations of this agent. Heat can be pro- 

 duced from work or electric energy from heat, but energy itself can 

 neither be produced nor destroyed ; it can only change the form of its 

 manifestations. Expressions such as "energy production," rather 

 frequently used by biochemists, are therefore unsound. The law of 

 conservation of energy includes, as a special case, the fundamental 

 law of thermochemistry mentioned above. 



On the basis of the law of conservation of energy, or the first law 

 of thermodynamics, any form of energy may be measured in terms of 

 any other. Table I gives the conversion factors for various units of 

 energy. 



B. FIELDS OF APPLICATION 



For biophysics, calorimetry is applied in research on heat transfer 

 of organisms. Of equal importance is the application of calorimetry 

 for the measurement of other forms of energy. Transformations to 

 any form of energy but heat are as a rule incomplete. The transfer of 

 any form of energy to heat, on the other hand, can ordinarily be per- 

 formed easily and completel3^ This unique position of heat among 

 the various manifestations of energy makes calorimetry particularly 

 suitable for the measurement of other forms of energy. Of special 

 interest for biophysicists are the calorimetric measurements of radiant 

 energy and of chemical energy. 



1. Heat Transfer 



The knowledge of animal heat transfer is important for the choice 

 of standard clothing. It is widely applied also in the design of insula- 

 tion and of heating and cooling devices in houses for man and ani- 

 mals. Builders of hatcheries, brooders, and poultry houses are par- 

 ticularly interested in the rates of heat transfer of the birds. Parti- 

 tional calorimetry — that is, the measurements of radiation, convec- 

 tion, conduction, and water evaporation as parts of total heat trans- 

 fer — proves especially helpful. The knowledge of the thermostatic 

 characteristics of farm animals will be of importance not only for the 

 care and management of the herds, but also in the selection for breed- 



