BASAL METABOLISM. 49 



obtained with the same subject awake and in complete muscular repose. 

 Even though the body be muscularly quiet while lying on a couch or 

 bed and the voluntary muscles be perfectly controlled, the involuntary 

 muscles, such as those of circulation, digestion, and respiration, are 

 active. These involuntary muscles continue their work in deep sleep 

 at a somewhat lower level. 



A second factor which definitely affects the base-line is previously 

 ingested food. It has been clearly demonstrated by practically all of 

 the earlier workers that an increased metabolism follows the taking of 

 food, particularly when protein and certain carbohydrates form a part 

 of the diet. If possible, therefore, we must find a point in the digestive 

 cycle at which the metabolism will not be influenced by the previous 

 diet, but which will be prior to the severe drafts upon the body glycogen 

 that have been found in researches at both Wesleyan University and 

 the Nutrition Laboratory during several days of strict fasting. It 

 seems to be the consensus of opinion of nearly all experimenters in this 

 line of research that with normal man, unless the last meal has been 

 excessively rich in protein, active digestion ceases 12 hours after the 

 ingestion of food and the metabolism has then reached essentially the 

 normal level, i. e., the level prior to the taking of food. This has been 

 demonstrated in a number of researches, particularly those of Magnus- 

 Levy. 1 Hence it is now the custom of most experimenters to study the 

 basal metabolism by making experiments 12 or 14 hours after the last 

 meal or, as Benedict and Cathcart have expressed it, with the subject 

 in the "post-absorptive condition/' 2 and to assume that the influence 

 of previously ingested food will in this way be eliminated. 3 The 

 metabolism at this time, however, does not always represent the mini- 

 mum metabolism, as will be seen in a later discussion. 



At this point we may ask: What is the lowest metabolism? If in a 

 normal state of nutrition the voluntary muscles of the body are so per- 

 fectly controlled that there is no visible movement, the muscles so 

 relaxed as to diminish the muscle tonus, the pulse rate and the respira- 

 tion rate depressed to the lowest point, and there is no food in the ali- 

 mentary tract, and furthermore, if the subject is in deep sleep, we may 

 expect to obtain the minimum metabolism for that particular subject. 



The ideal conditions outlined for obtaining such a low metabolism are, 

 as a matter of fact, not readily secured with the majority of subjects. 

 If in studying the influence of a superimposed factor upon metabolism, 

 the measured base-line can be relied upon as uniform, it is not necessary 

 that the lowest metabolism be secured. In experiments which involve 

 relatively slight changes in metabolism, however, the lower the metab- 

 olism which can be secured for the base-line, the greater will be the 



Magnus-Levy, Arch, f . d. ges. Physiol., 1894, 55, p. 1 ; see especially p. 23. 

 2 Benedict and Cathcart, Carnegie Inst. Wash. Pub. No. 187, 1913, p. 71. 

 'Benedict and Higgins, Am. Journ. Physiol., 1912, 30, p. 217. 



