114 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



USE OF AVERAGE BASAL VALUES FOR COMPARISON. 



A considerable amount of experimental evidence has accumulated 

 regarding the relationship of the average basal values of different 

 individuals. 1 The comparison of the results obtained with different 

 subjects has been much discussed, together with the varying effects 

 upon them of the factors influencing the basal metabolism, such varia- 

 tions depending upon the different conditions of nutriment and environ- 

 ment. Here, however, we are particularly interested only in those 

 factors which influence the basal metabolism of a single individual. 

 The question arises : To what extent is it possible to determine the basal 

 metabolism of a subject and assume that this value is constant and may 

 be logically used as a general base-line for food experiments subse- 

 quently carried out? 



When several basal experiments have been made with a subject, 

 and a number of closely agreeing results have been obtained for that 

 particular day, many investigators use this average basal value for 

 comparison with results obtained on subsequent days without further 

 comment. The short-period method admits of the duplication of 

 experimental periods for comparison in securing an average basal 

 value, but it is by no means certain that the general use of such a value 

 is the wisest or the most satisfactory procedure. 



It is obvious that the metabolism will be somewhat affected by a 

 material alteration in the body-weight, such as may take place in the 

 course of a year or, with a growing individual, in a very much shorter 

 space of time. A base-line determined under materially different 

 weight conditions may not therefore be used for general comparison. 



Furthermore, seasonal variations may be possible. For example, 

 we may ask whether a base-line determined in the winter may be logi- 

 cally used for comparison in the summer. One of the most striking 

 illustrations of seasonal variation was given in some observations made 

 at the Massachusetts General Hospital upon Palmer. 2 With essen- 

 tially the same body-weight, the subject showed in summer a total heat 

 production of 1,797 calories, 19.2 calories per kilogram of body-weight, 

 and 707 calories per square meter of body-surface; in winter he had a 

 total heat production of 2,004 calories, 21.4 calories per kilogram of 

 body- weight, and 789 calories per square meter of body-surface. 



The question of possible seasonal variation has also been considered 

 in connection with the results of our short-period experiments. To this 

 end the values obtained for the consumption of oxygen per minute in 

 the individual months have been averaged in table 46 for each subject 

 who was studied during a period of at least 1\ months. The longest 

 period of time during which experiments were made was that for 



'Benedict, Emmes, Roth, and Smith, Journ. Biol. Chem., 1914, 18, p. 139; Benedict, ibid., 



1915, 20, p. 263. 

 2 Palmer, Means, and Gamble, Journ. Biol. Chem., 1914, 19, pp. 242 and 243. 



