430 Influence of Inanition on Metabolism. 



(3) the heat production, which varies directly with the muscular activity. 

 By comparing the estimated amount of muscular activity (derived by the 

 above methods) with the quantities of water-vapor in respiration and perspira- 

 tion, any relationships existing between them may readily be observed. 



As the result of observations in a large number of experiments on muscular 

 work, 107 it has been found that excessive muscular work produces an enormous 

 increase in the water vaporized from the lungs and skin. It has been definitely 

 shown that when sensible perspiration appears, there is a noticeable increase 

 in the water-vapor output accompanying muscular work. On the other hand, 

 when no extraneous muscular exercise is taken, it is difficult to demonstrate 

 the influence of minor muscular activity on the water-vapor output. In all 

 the experiments here reported, the subjects were practically at rest, with the 

 single exception of the second period of experiment No. 71 when the subject 

 rode a bicycle ergometer for 10 minutes. There was no visible perspiration, 

 however, in this short period of exercise. The marked differences in the elimi- 

 nation of water-vapor, therefore, must be explained by some factors other than 

 marked muscular activity, for the daily routine of the subjects was not unlike, 

 as is seen by comparing the records of body movements. However, that there 

 were marked differences in the sum total of bodily activities, not only in 

 experiments with different subjects but also on different days of the same 

 experiment, is shown in the discussion regarding muscular activity. A com- 

 parison of the relative amounts of muscular activity there estimated with the 

 amounts of water-vapor leaving the lungs and skin shows that there is a dis- 

 tinct relation between even the minor differences in muscular activity as es- 

 timated and the actual water-vapor output. 



The problem is, however, not as simple as it first appears, for on the 

 assumption that even minor differences in muscular activity produce wide 

 variations in the total quantity of water vaporized, we should expect to find a 

 much smaller vaporization of water during the night period of all the experi- 

 ments, when the subjects were asleep, than during the day period. This is 

 not invariably the case as is shown in the discussion in the next section. 



The periodic elimination of water-vapor. Opportunity was offered in the 

 experiments here reported to study the periodicity of the output of water-vapor 

 during the experimental day. The experimental periods were all of 2 hours' 

 duration. Since unusual care was taken in the measurement of the water-vapor 

 and comparatively small changes in the weight of the bed, bedding, etc., 

 occurred in a majority of the experiments, the results give an accurate measure 

 of the water-vapor output for the different periods of the day. The methods 

 of applying the corrections for the changes in weight of the bed and bedding 

 have been explained previously. The results for both the fasting and the 

 food experiments are given in detail in table 219. In this table is recorded the 



107 U. S. Dept. Agr., Office of Expt. Sta. Bui. 136. 



