200 VITALITY AND EFFICIENCY WITH RESTRICTED DIET, 



Furthermore, a great many people spend over one-half of their time 

 either in bed or sitting quietly with minimum muscular activity. 

 Since sitting involves an increase of but 10 per cent above the basal, a 

 considerable proportion of the 24 hours of the day may be properly 

 represented either by basal metaboHsm or by a slight percentage 

 above it. 



For the great needs of this Nation the fundamental basal metabolism 

 per 24 hours is a factor of prime importance. For the physiologist 

 the basal metabolism has even a greater refinement of definition. 

 Theoretically, the basal metabolism is the minimum metabolism, but 

 this is rarely observed in man, and the minimum metabolism compati- 

 ble with life may be very much lower than the ordinary basal metabo- 

 lism of a normal individual. However, it is conomonly assumed that 

 the basal metabolism, measured during periods of complete muscular 

 repose, 12 hours after the last meal, and with the subject in deep sleep, 

 represents the minimum, normal basal metabolism. The factors 

 influencing this may be divided into two classes: (1) extraneous or 

 superimposed factors, such as muscular work and the ingestion of 

 food, and (2) inherent factors, such as sex, age, composition of the 

 body (proportion of muscular tissue), condition of sleep versus awake, 

 and disease. Many of these may pertain to the same individual at 

 different periods of life. In studying groups it is important to note the 

 influence, if any, of sex, age, state of being awake or asleep, and also the 

 composition of the body, i. e., a. study of individuals who are distinctly 

 fat as compared with those who are distinctly thin. Finally, there are 

 ever-increasing data with regard to the influence of disease upon metab- 

 olism, but the opportunity is infrequent for studying this with a single 

 individual, for rarely can a subject be observed in health and again 

 subsequent to acquiring a disease, such as diabetes and hyperthy- 

 roidism. One must therefore resort to a study of groups of normal 

 individuals and compare the results with groups of individuals having 

 the disease. But a study can be made with a single individual on the 

 influence of sleep, the digestion of food, and muscular work. All three 

 factors influence metabohsm in an increasing degree. So, by insisting 

 upon complete muscular repose and the absence of food, the two most 

 prominent factors influencing basal metabolism are eliminated. There 

 is still left sleep. Thus far the studies on metabolism in deep sleep are 

 extremely few and are practically limited to observations with the 

 respiration-chamber method. 



VARIATIONS IN NUTRITIONAL LEVEL. 



An analysis of the factors affecting metabolism shows that the 

 influence of food and muscular work is always in the same direction, 

 I. e., to increase metabolism. Are there any conditions in which 

 metabolism can be depressed? In other words, is the basal metabolism 



