CALORIFIC REQUIREMENT AND THE SURFACE-LAW 589 



80 per cent, with normal infants, cannot be considered as a physiological 

 law." Benedict draws attention to the great importance of specific 

 Stimulators of Metabolism, which may be contained in the diet or in 

 the products of the activity of certain tissues. Thus after prolonged 

 severe Muscular Exertion the metabolism is stimulated for a long period 

 following the cessation of exercise and the consumption of foodstuffs 

 for the production of mechanical work. Yet the ratio of bodily sur- 

 face to volume has undergone no change in consequence of the exercise, 

 nor has the temperature of the body risen. Whatever may be the 

 mechanism which brings it about it is clear that products of muscular 

 exercise (and the same is true of acidosis) induce a stimulated combus- 

 tion of foodstuffs, and therefore, in the absence of ingested food, an 

 increased destruction of tissue. 



FIG. 50. Chart, prepared by Du Bois, showing the basal metabolism as measured in 

 calories produced per square meter of body-surface per hour from birth until the age 

 of eighty-five years in human males. Between maturity and the eighty-fifth year 

 there is a gradual fall in the intensity of metabolism of 13 per cent. (After Lusk.) 



Benedict infers that the total metabolism, or metabolism at rest with- 

 out food, is determined by two main factors; the first the mass of 

 Protoplasmic Tissues (parenchyma) and the second the variable concen- 

 tration of specific Stimulators of Metabolism in the tissues. It was, 

 in fact, assumed by Voit that the total metabolism is actually propor- 

 tional to the mass of cellular as distinguished from Sclerous Tissues 

 in the body and this view is supported by the steady decrease in 

 metabolism which is characteristic of the period between maturity and 

 old age in man (Fig. 50). The increase in basal metabolism per unit 

 of weight or surface which occurs to a very striking degree during the 

 first year of post-natal growth is, however, only to be interpreted by 

 also taking into consideration the second factor suggested by Benedict, 

 namely the variable concentration of stimulators of metabolism which 

 determines the Metabolic Rate of the tissues. Ihe rise in metabolism 

 which occurs in early growth and just before puberty, therefore, indi- 

 cates an accumulation of stimulators of metabolism which are not 

 improbably the Endogenous Catalyzers of growth. 



