NUTRITION LABORATORY. 



The results are given in table 2. 



Tabi,E 2. — Effect of Increasing External Work on Body Efficiency. 



191 



Aside from the value for the increase from 0.7 to 0.8 ampere, i. e., 26 per 

 cent, all the results are remarkably constant, showing that the increase of 

 load does not materially affect the efficiency of the body as a machine. Under 

 all the conditions of work in these experiments the body was able to transmit 

 about 21 per cent of the increased heat incidental to the increased load into 

 heat of external muscular work. 



With such a striking influence of muscular activity upon metabolism, it 

 became of great interest to note the influence of mental work on metabolism. 

 Recognizing the difficulties of securing sustained mental work during an ex- 

 perimental period of 2 to 3 hours, the best results were secured by studying 

 the metabolism of a large number of college students while taking their mid- 

 year examinations inside of the respiration chamber. During this period it 

 was reasonable to assume that there was sustained mental effort. Control 

 experiments were made several days later, and at the same time of the day 

 and as nearly as possible under like conditions. The control experiments 

 were so arranged as to include plain copying with the pen, with as little mus- 

 cular work as possible, and the mental activity was reduced to the minimum. 



Twenty-two experiments were made, and the results, together with the 

 results of 22 control experiments, are given in table 3. There are, indeed, 

 slight mathematical differences in the averages of the two periods, but a 

 careful examination of the tabulated data in the original report shows that 

 the variations between experiments were so wide that they leave no possible 

 opportunity for assuming that mental work per se exercises any influence 

 upon metabolism. 



Tabi^e 3. — Results of Experiments upon the Effect of Mental Work on Metabolism. 



13— YB 



