36 POWER AND THE PLOW 



B.t.u. for hay and grain alone. The winter work being usually 

 of very light nature, it is probable that out of 100 pounds of 

 energy fed, less than one pound is recovered as work. Obvi- 

 ously, these figures can be regarded as only approximate, 

 since no tests have been made of the efficiency of the animal 

 under the above conditions. They furnish, however, striking 

 exceptions to the general idea as to the efficiency of the 

 animal as a machine. 



If the energy which passes unchanged through the animal 

 body; the energy required to chew and digest food; the energy 

 required to maintain vital processes and body heat; the energy 

 required for moving the animal body if all this be sub- 

 tracted from the original heat value of the food, and only the 

 energy liberated in the animal muscle during work be taken 

 as a basis, an efficiency of 25 to 40 per cent, may be computed. 

 This has been the foundation for the statement that the animal 

 is a much more efficient machine, viewed solely from the stand- 

 point of transforming fuel into energy, than any made by man. 

 This is not always the case. Under farm conditions, where 

 animals are worked only a few hours per day, on the average; 

 where feeding is usually unscientific and wasteful; and where, 

 according to T. H. Brigg, an English scientist, the horse 

 often labors under conditions where 50 per cent, of his en- 

 ergy is lost, the horse becomes a very inefficient motor, at 

 least as regards the conversion of chemical energy into 

 useful work. 



Neither animals nor engines are worked to their full capacity 

 on the ordinary farm, but there is this difference: the fuel 

 consumption of the engine is measured by the amount of work 

 done, plus only the energy required to overcome friction within 

 the engine itself during the time at work, with nothing for 

 maintenance during long periods of idleness. Speaking of the 

 horse at rest, Professor Armsby says: "The case is like that 

 of an engine run with no load, which still requires a certain 

 amount of fuel to keep it running." Only rarely does 



