NORMAL PROCESSES OF ENERGY METABOLISM 607 



V. Basal Metabolism 



By way of summary of the preceding sections one may say that the 

 three factors which have most to do with determining the level of the 

 energy metabolism in the normal suhject are muscular activity, external 

 temperature and food. A suhject removed from the influence of these 

 three factors would he (a) completely resting; (h) at a comfortable tem- 

 perature; (c) and would he observed several hours after the ingestion of 

 food. The metabolism under these conditions would correspond to the 

 minimal functional activity of the body and for this reason has been 

 called basal metabolism after Magnus-Levy ( ft) (Grundumsatz). The 

 term "maintenance metabolism" (Erhaltungsumsatz) has also been given 

 by Loewy(a), and the term "standard metabolism" is preferred by 

 Krogh(c) who points out that even under complete suppression of mus- 

 cular activity the metabolism of the heart may amount to as much as 4 

 to 15 per cent of the total metabolism of the body, and the metabolism of 

 respiration to a like amount. The true basal metabolism according to 

 Krogh w r ould be found by deduction of those quotas assignable to the 

 heart muscle and the muscles of respiration. 



Whichever term is applied it should be understood that this minimal 

 metabolism is the line of reference for the measurement of the various 

 functional increases such as that due to food or to muscular work. The 

 term basal metabolism will be employed in this chapter as being considered 

 more appropriate than either of the other terms suggested. It is useless 

 in the writer's opinion to use as the reference line a minimal metabolism 

 lower than that which is attainable in the normal subject. It is, however, 

 a fair question whether the metabolism of sleep should be taken as the 

 basal metabolism in man, or, whether the condition defined by Benedict 

 and his co-workers as the post-absorptive condition combined with com- 

 plete muscular rest gives the better line of reference. F. G. Benedict has 

 shown that in a fast of 31 days the metabolism during deep sleep may be 

 as much 13.2 per cent lower than the metabolism of the same subject while 

 awake but lying perfectly still. In this series the increased metabolism 

 could not be attributed to muscular activity for a comparison of the graphic 

 records showed that the degree of muscular repose was even more nearly 

 perfect in the morning experiments while waking than in the night experi- 

 ments during which the subject slept in the bed calorimeter. There was 

 also no question of influence of food in the alimentary tract; for during 

 the entire period of 31 days the subject ate absolutely no food and drank 

 only about 900 c.c. of distilled water daily. It is fairly certain, therefore, 

 that the only cause of difference was that state of the nervous system 

 which we recognize as sleep. Presumably the lower metabolism in this 

 state is due to the more complete suppression of muscular activity owing 



