WORK PRODUCTION 551 



shows of course the expenditure in the latter exclusive of that 

 required to maintain the body upright (work of standing), 

 or what may be called the net expenditure. 



On the average of thirty-five trials upon locomotion at a walk, 

 Zuntz and Hagemann found the net expenditure of energy by 

 the horse per meter of horizontal locomotion (after correcting 

 in the manner described in the next paragraph for the small 

 amount of work of ascent due to the fact that the tread power was 

 not exactly horizontal) to be as follows per kilogram of weight : 



At a speed of 78 meters per minute . . . 3256 gram calories 

 At a speed of 90.16 meters per minute . . . 3666 gram calories 

 At a speed of 98.11 meters per minute . . . 3929 gram calories 



The actual amount of mechanical work done in horizontal 

 locomotion and converted into heat cannot be measured di- 

 rectly. Zuntz and Hagemann, however, have computed it by 

 means of a formula proposed by Kellner 1 and by comparison 

 with the figures just given, compute a net efficiency of about 

 35 per cent. 



653. Work of ascent. The animal may also perform work 

 by drawing or carrying a load up a hill. Taking the simpler 

 case of carrying a load, the total output of energy would be 

 expended for three purposes, viz., maintenance (resting value), 

 locomotion, and lifting the weight of the load plus body in op- 

 position to gravity. Zuntz separates the two latter factors from 

 each other by a comparison of two experiments in which the ratio 

 of distance traveled to ascent, i.e., the angle of ascent, differs. 



Thus in the thirty-five trials with nearly horizontal locomo- 

 tion the average energy output per kilogram of live weight, after 

 deducting the maintenance requirement, was 0.4035 gram calo- 

 ries per meter traveled. During the same time, however, the body 

 was lifted through 0.4395 centimeters, equivalent to 0.004395 

 kilogram meters of work of ascent per kilogram of live weight. 

 In thirteen experiments on ascending a moderate grade, the 

 average energy expended in excess of maintenance per kilogram 

 live weight was 1.0795 gram calories per meter traveled, while 

 the work of ascent was 0.107041 kilogram meters per kilogram. 

 Letting x equal the energy per kilogram required for one meter 

 of horizontal locomotion and y the energy required for the 



1 Landw. Jahrb., 9 (1880), 658. 



