Investigations Concerning the Horse. 259 



saving of nutrients, such saving being greatest when the down grade 

 was about 5 ft. in 100. If the grade was steeper than this, the horse 

 expended energy in bracing himself to check too rapid progress. 

 When the downward grade reached 10 ft. in 100, as much energy was 

 expended as when traveling on a level, and on a still steeper down 

 ^rade the amount of energy expended was greater than that expended 

 on the level. 



399. Lifting the body. Zuntz found that a horse walking at a 

 speed of 3.1 miles per hour on a tread power having a grade of 10.7 

 feet in 100 expended 1.89 Cal., or 0.00189 therm, of energy per ft.- 

 ton in raising the body against the force of gravity This sum is in 

 excess of the energy which would have been expended if the horse 

 had been moving on a level course. It means that in ascending a hill 

 having a grade of 10.7 ft. per 100, the 1000-lb. horse does 1 ft.-ton of 

 work in raising his body 2 ft., expending 1.89 Cal. in performing 

 such work. On this grade 34 per ct. of the energy expended ap- 

 peared in the external work done in raising the body. The rest of 

 the energy used up produced no external work but was changed into 

 heat. When moving at a speed of 2.8 miles per hour on the steeper 

 grade of 18.1 ft. in 100, 2 per ct. more energy was expended per 

 ft.-ton than upon the gentler grade. 



400. Carrying a load. When carrying a load the horse expends 

 energy in addition to that required for merely moving his body, as 

 the following by Zuntz shows. Upon loading the saddle with about 

 275 Ibs. of lead plates, 8 per ct. more energy was expended when 

 walking at a speed of 3.4 miles an hour than when no load was car- 

 ried. Trotting at a speed of 6.9 miles per hour with the load caused 

 an expenditure of about 10 per ct. more energy than trotting at the 

 same speed with no load. 



401. Draft. Zuntz found that after deducting the energy neces- 

 sary for moving the body along a level course, 2.1 Cal., or 0.0021 

 therm, was required per ft.-ton of draft performed by the horse. 

 Of the total energy used up in the body for performing a given 

 amount of draft, only 31 per ct. resulted in draft, as shown by the 

 dynamometer, the remainder taking the form of heat. We thus see 

 that in performing draft the horse is not able to turn as large a part 

 of the energy used up in his body into mechanical work as he does in 

 moving his body along a level course or in raising it against the 

 force of gravity. In other words, he is able to perform mechanical 

 work less economically in hauling a load than in moving his own 

 body. In drawing a load up a grade of 8.5 ft. in 100 but 23 per ct. 



