BASAL METABOLISM. 47 



action theory of Rubner. Clear-cut evidence for or against these 

 theories is, in spite of the great mass of experimental data, not readily 

 found. Writers are about evenly divided between the two theories. 

 Those upholding the Verdauungsarbeit theory have the distinct advan- 

 tage of having a definite process to consider. On the other hand, the 

 definition of the specific dynamic action in Rubner's theory, and more 

 particularly the application of the theory, is somewhat obscure and has 

 led to a great deal of confusion. It should be stated, however, that 

 few theories regarding the physiology of digestion have stimulated so 

 much excellent research work as has the specific dynamic action theory. 



BASAL METABOLISM. 



To study the influence upon metabolism of such a factor as the inges- 

 tion of food, the energy requirements of the quiescent body prior to 

 the ingestion of the food must be known, for otherwise the measurement 

 of metabolism after food can have no comparative significance. Thus 

 the whole problem of demonstrating the influence of the ingestion of 

 food upon metabolism depends upon two vitally important processes: 

 (1) the establishment of a suitable base-line, and (2) the accurate meas- 

 urement of metabolism following the ingestion of food. 



While at first sight it might be assumed that the establishment of a 

 base-line is relatively simple, close analysis shows that this is far from 

 being the case. In the first place, there is no normal value for either 

 male or female adults that may be taken, a priori, as a base-line for any 

 subsequent measurements. Various attempts have been made to 

 establish more or less crude "standard" values and results have been 

 obtained which give rough indications of the major changes in metabo- 

 lism due to disease, food, or muscular work. These so-called standard 

 values can not, however, be used for any quantitative study of the 

 influence of a specific factor upon metabolism. Each series of measure- 

 ments accordingly demands its own basal determination. 



In determining basal values, the conditions should preferably be as 

 much as possible like those obtaining during the comparison experi- 

 ments. Thus, in any research on the effects of bicycle riding, it may be 

 fairly argued that the base-line should be determined not when the 

 subject is lying in deep sleep, but when he is sitting in the ordinary 

 position occupied by a bicycle rider. Again, when the work of hori- 

 zontal walking is studied, the base-line would not logically be that 

 obtained during deep sleep, but would be a value secured with the 

 subject standing in readiness for walking. 



The degree of care necessary in the selection of a base-line is depend- 

 ent upon the size of the increment in the metabolism due to the super- 

 imposed factor. By active muscular work it is perfectly possible for 

 a well-trained athlete to increase his basal metabolism tenfold or more, 



