THE ANIMAL AS A MOTOR. 



49 



of performing more work than the food would seem 

 competent to do. In these cases it would seem very 

 possible that the observed excess may come of con- 

 sumption of tissue in addition to food ; the waste being 

 gradually repaired during a later period of prolonged 

 rest, with food-consumption above the normal rate. 



Dr. Flint, who paid much attention to this subject, 

 concluded, as the result of the study of the working of the 

 muscular system of a celebrated pedestrian (Weston), 

 about 1870, during a walk of 318 miles in five days, 

 weighing all foods and excretions and noting their com- 

 position, that it is as yet impracticable to intelligently 

 compare the force-value of foods with the work of the 

 muscular system ; that such estimates, as now custom- 

 arily made, account only for a part of the work, even 

 leaving out of consideration the energy of other (vital 

 and nervous) actions ; that exercise always results in 

 waste of muscular tissues, which may not be repaired at 

 the time ; and he also believes that the source of energy 

 is the wasted tissue, and, indirectly only, the nitrogen- 

 ized food which supplies the waste. 



Dalton takes the production of heat in the body at 

 rest, per hour, as about 1.28 British heat-units per pound 

 of its weight. Houghton estimates the work done in 

 walking at one twentieth of the weight of the body in 

 pounds multiplied by the number of feet walked per 

 hour ; and it would seem possible, from Flint's compu- 

 tations, that about ten per cent of the total energy- 

 expenditure takes place in the brain and nervous sys- 

 tem in the case of man, although that author does not 

 so take it.* The processes involved in the operation 



* Source of Muscular Power, pp. 100-103. 



