196 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



conditions, i, e., "basal metabolism," plus the fuel required for extra- 

 neous muscular activity. The latter varies with the external activity of 

 the individual, for obviously the sedentary college professor requires 

 much less energy in his diet than the Canadian lumberman. 



Since basal metabolism has not, at present, known, definite relation- 

 ships to the state of well-being and the efficiency of the organism, other 

 criteria for judging the adequacy of the state of nutrition must be em- 

 ployed. The condition of the fundamental physiological processes and 

 of the more complex neuro-muscular processes which have a most 

 intimate bearing upon muscular and mental work are determinable by 

 well-attested laboratory techniques and in any comprehensive inves- 

 tigation should be considered. 



BASAL METABOLISM. 



The minimum demand for energy is the amount which is required for 

 the "basal metabohsm." The chief factors known to increase the vital 

 activity or metabolism of the body are muscular activity and ingestion 

 of food. If the former is precluded by enforced repose and the latter 

 is eliminated by observing the metabolism when the active processes of 

 digestion have ceased, i. e., with the subject in the post-absorptive 

 state, we obtain a value which may be considered to be the basal metab- 

 olism of that individual. 



While in this measurement of the basal metabolism the influence 

 of muscular activity and food are eliminated, there are other factors 

 which produce variation in the basal metabohsm of normal indi- 

 viduals. Among these the most obvious is body-size, as indicated 

 by height and weight. Age also influences the metabolism, for 

 elderly people of exactly the same height and weight as younger people 

 have a somewhat lower basal metabohsm. There is strong evidence 

 that during deep sleep the metabolism is perceptibly lowered. Severe 

 muscular work unquestionably has a stimulating after-effect upon the 

 metabolism which may persist for many hours after the work has 

 ceased. Furthermore, careful measurements of the basal metabolism 

 over a considerable period of time show that variations of no mean 

 magnitude occur even with the same individual, these averaging at 

 times as high as 13 to 14 per cent.^ The exact cause for these varia- 

 tions is not known. That they are seasonal is highly improbable. 

 Suitable analysis of the correlations for weight, height, surface, age, and 

 other factors which influence the metabolism can only be made from 

 measurements obtained with a large number of normal individuals.^ 



CONSTANCY IN BASAL METABOLISM. 

 The possibiUty of the basal metabohsm being a physiological con- 

 stant has been much discussed. Fro m the earliest measurements of 



1 Benedict, Journ. BioL Chem., 1915, 20, p. 263. 



* Harris and Benedict, Carnegie Inst. Wash. Pub. No. 279, 1919. 



