Mans Mechanical Efficiency in Work Performance. 395 



example, the main data, throughout termed " heat productions," include 

 frequently a larger quantity of heat than that dissipated from the experi- 

 mental subject as such, since they include an allowance made for any 

 additional heat stored in his body (an allowance assessed with reference to 

 the rectal temperature), and also include the heat dissipated from tbe experi- 

 mental machine (cycle) whenever, and to the same extent as, work is 

 performed upon it by the subject. It is clear that only such sums of the 

 total transformation of energy by the subject are of major physiological 

 interest, as alone equivalent to data obtained from examinations of the 

 exchange of oxygen and carbon dioxide in the concomitant process of 

 respiration, and to data obtained in any other fashion as to the oxidation of 

 material in the body. 



Then, again, it is necessary to define the usage of the term " efficiency," 

 since although at the outset of these experiments that usage was as far as 

 possible defined by the very nature of the experiments, occasion has since 

 arisen to utilise the term in an unanticipated way. Thus, originally,* they 

 were arranged to provide a determination of " efficiency " by the comparison 

 of increments in work performance with associated increments of heat 

 production, and that arrangement is very definitely continued in the data 

 under discussion, since the process of experiment was narrowed down to an 

 examination of numbers of individual subjects in two groups of experiments 

 (A and C), differing only from one another by an increment of work and its 

 consequences. Owing to an accident these groups were interrupted, and 

 later, after a complete overhauling of the calorimeter and its apparatus, 

 under improved conditions the same process was renewed, but the results of 

 this later series have been classified under Groups B and D. In either case 

 it was intended to deal finally with the question of efficiency by a 

 comparison of increments observed under similar experimental conditions 

 and it is to be dealt with best by making that comparison where those 

 •conditions were at their best, that is, in the later pair of groups (B and D). 

 Utilised in reference to such a comparison, there is not much chance that 

 any misunderstanding can arise as to the meaning of " efficiency." When 

 later the, usage of the term is expanded, as first when the efficiency 

 prevalent in the performance of the whole of the external work is 

 considered (as distinguished from the increment) in each of the experiments 

 of Group B and of Group D, even at that stage the term will probably not 

 be misunderstood, since it will be clear that the work done is then being 

 •compared to that fraction of the heat production which includes it, and 

 which is associated with its performance and with nothing else, not even 

 * 'Brit. Assoc. Eeports,' p. 289 (1912;. 



2 K 2 



