WORK PRODUCTION 547 



a comparison of the brake horse power with the steam con- 

 sumption. 



But the body katabolizes matter and liberates energy for 

 other purposes than the performance of external work, i.e., it 

 has a maintenance requirement for the support of its internal 

 work (341, 342) analogous in some respects to the energy re- 

 quired to run an engine without load. The subject of Benedict 

 and Cathcart's experiment produced during rest (lying on a 

 couch) 1.09 Cals. of heat per minute. If this maintenance re- 

 quirement be subtracted from the total energy output during 

 work there is left 5.23 Cals., as the additional energy output 

 required for the performance of the 1.02 Cals. of measured exter- 

 nal work. % Computed in this way an efficiency of 1.02 -f- 5.23 

 = 19.5 per cent results. This has been called the net efficiency. 

 It shows the utilization of that portion of the energy output 

 which is expended in the physiological processes required for 

 the production of external work as distinct from the various 

 forms of internal work included in the maintenance requirement. 

 In computing the net efficiency in this way difficulty arises in 

 deciding upon the proper deduction to be made. Thus in an 

 experiment like that just cited, one may subtract from the 

 total energy output of the body during work, not only the 

 energy expenditure for maintenance during rest but likewise 

 that caused by sitting on the ergometer and causing it to rotate 

 without load, and the remainder may be regarded as the energy 

 metabolized for the performance of the useful work. The 

 total output of energy being 6.32 Cals. per minute during the 

 work, it was determined that the same subject metabolized 1.13 

 Cals. more energy per minute when riding without load than 

 when at rest. The added load in the work experiment, there- 

 fore, required the expenditure of 6.32 (1.09 -f- 1.13) = 4.10 

 Cals. per minute for the performance of 1.02 Cals. of 

 work, from which an efficiency of 24.9 per cent may be com- 

 puted. Similarly, in experiments with the work horse one may 

 subtract the energy expended during horizontal locomotion in- 

 stead of that metabolized during rest and compare the remainder 

 with the useful work done. 1 



1 For a discussion of the various base lines for the computation of efficiency, 

 compare Benedict and Cathcart's publication already cited, pp. 112-136, and also 

 Reach, Biochem. Ztschr., 14 (1908), 430; Landw. Jahrb., 37 (1908), 1053. 



