THE BALANCE OF NUTRITION 235 



The outgo of work and heat from the body 



325. Outgo of kinetic energy. The feces, urine, combus- 

 tible gases and cutaneous excreta carry off chiefly unused 

 chemical energy. 1 To recur to the illustration of the internal 

 combustion motor, they are comparable with losses due to 

 leakage or incomplete combustion of the fuel. The energy re- 

 maining after these losses have been met, i.e., the metabolizable 

 energy, may be converted in part into mechanical work and 

 in part into heat. 



When an animal performs work, whether in drawing a load, 

 carrying a rider, operating a tread power or simply lifting 

 the weight of his own body at each successive step, a portion, 

 although on the whole a relatively small percentage, of his total 

 income of chemical energy is expended in moving objects, i.e., is 

 converted into kinetic energy. The kinetic energy thus pro- 

 duced may be measured in accordance with the general methods 

 described in a previous paragraph (313), usually by conversion 

 into gravitation energy and measurement in gravitation units, 

 i.e., the gram meter, kilogram meter or foot pound. 



326. Outgo of heat. The outgo of heat which common 

 experience teaches is continually taking place from the bodies 

 of men and of animals represents a very considerable share of 

 the total income of chemical energy. It has been computed 

 that if the heat produced by the average healthy man could 

 be prevented from escaping from the body it would in a single 

 day raise it to a pasteurizing temperature, while in the course 

 of a month at the same rate, the temperature would be raised 

 approximately to that of melting cast iron. 



327. Animal calorimeters. The great variety of animal 

 calorimeters which have been devised for the purpose of measur- 

 ing the heat production of living animals have been of three 

 general types, which may be designated as water calorimeters, 

 latent heat calorimeters and emission calorimeters. 



Water calorimeters are those in which the heat is imparted 

 to a known quantity of water, the rise of temperature of which 

 is measured, i.e., they employ the first of the two methods of 



1 The heat which they also carry off is included in the total outgo of heat con- 

 sidered in the next paragraph. 



