Variations in Metabolism. 251 



during the morning period from 7 a. m. to 1 p. m. the muscular activity would 

 be greater than during the night period, but the important point here is that 

 there was sufficient muscular activity to increase the pulse-rate during the 

 forenoon by a certain percentage. Was or was not the metabolism increased by 

 a similar or proportional percentage? It is only on the basis of variations in 

 pulse-rate that the values expressed in table 105 are to be considered. In ex- 

 periments with the same subject it is seen that the increase in metabolism is 

 roughly proportional to the increase in pulse-rate. 



METABOLISM DURING DIFFERENT ACTIVITIES REFERRED TO A 



COMMON STANDARD. 



From the results of a large number of experiments on different individuals, 

 an average figure for the metabolism in different states of bodily activity may 

 be obtained. It is clear, however, from all the tests here reported that each 

 individual is to a certain extent a law unto himself. With a given body-weight 

 and height, the metabolism is approximately constant under conditions of like 

 bodily activity. One of the greatest difficulties in attempting to estimate the 

 metabolism of an individual during the day is not the determination of the 

 body-weight, or the height, or the general personal impression of the physical 

 characteristics of the individual, but the striking variations in muscular 

 activity, particularly the minor muscular activity. If each person were sub- 

 jected to a certain vigorous muscular test and required to perform a certain 

 amount of external muscular work, such as riding a bicycle-ergometer, the 

 total katabolism could be estimated with great accuracy. It is the minor mus- 

 cular movements, muscular tonus, involuntary muscular movement, pulse-rate, 

 respiration-rate, and blood-pressure that influence the total katabolism, each in 

 a small way, but all in a cumulative degree that interferes seriously with any 

 attempt to compute the exact katabolism. 



By far the most satisfactory basis for comparing different individuals is 

 during sleep, for as has been seen in all the comparisons heretofore made, the 

 variations from the normal are smallest during the sleeping period. Even 

 when the subjects are asleep, however, noticeable variations are found and 

 these can probably be considered, in large part, as a true index of the variations 

 in muscular activity with the different individuals during sleeping hours. 

 Under the present conditions of experimenting, where the pneumograph is used 

 simply to record the respiration rate and minor bodily movements, such a 

 method of approximating the muscular activity in different experiments is 

 readily obtained. This procedure was not, however, in vogue at the time these 

 experiments were made and hence we have not a proper comparison. 



PERCENTAGE VARIATIONS IN METABOLISM DURING DIFFERENT ACTIVITIES AS 



COMPARED WITH SITTING. 



These experiments were all planned with a view to studying a large number 

 of individuals, and the importance of duplicates with the same individual,, or 

 of so planning the experiments as to study certain definite points, was not 



