I9I0.] WORK ON NUTRITIVE PROCESSES. 153 



their examinations in the respiration calorimeter.^ The chamber 

 is large, fairly well lighted, quiet, with a good ventilation and 

 every possible convenience for quiet, sustained mental effort without 

 distractions. The men entered into the experiments heartily and 

 twenty-two such experiments were made. In order to control the 

 experiments and give us a basis for comparison, the same men 

 were on subsequent days placed in the calorimeter for the same 

 length of time, during which period no mental work was done and, 

 indeed, we went so far as to attempt to eliminate the results of the 

 muscular work of writing by giving them plain copying to do on 

 paper in the control period. By this means we were able to com- 

 pare the results of the experiments with mental work with the con- 

 trol experiment. During these mental work experiments, the men 

 were encouraged to note down all their personal impressions. 

 Some of the observations were very interesting. Several men said 

 it began to grow cold and then to grow warm, while as a matter of 

 fact, the temperature of the chamber did not vary by more than 

 two or three hundredths of a degree. Other men noted that they 

 perspired freely during the examination period and that they had 

 been under a tremendous strain and effort. 



TABLE III. 



IMetabolism During Mental Work. 



(Quantities per hour.) 



Examination Period. Control Period. 



Carbon dioxide 33.4 grams 32.8 grams 



Oxygen 27.3 grams 25.9 grams 



Water vapor 39.2 grams 37.8 grams 



Heat 98.8 calories 98.4 calories 



Averages of 44 experiments. 



But all of these personal impressions fall wholly out of con- 

 sideration when we compare the results of the experiments with the 

 students during the examination period and during the control 

 period. There was practically no difference between the results with 



^ For a detailed discussion of these experiments see Benedict and Car- 

 penter, " Muscular and Mental Work and Efficiency of the Body as a 

 Machine," United States Department of Agriculture, Office of Experiment 

 Stations, Bui. 208, 1909. 



