28 APPLIED PHYSIOLOGY 



over of energy in the body, there is a strong presumption 

 that such differences exist. It is tempting to suppose, 

 for instance, that the vital activity of the cells is greater 

 in some persons than in others. A feeble vitality of the 

 cells might explain the undoubtedly greater tendency to 

 obesity in some persons and families than in others. 

 From a physiological point of view such persons might 

 be regarded as very economical machines, their economy 

 being effected by a diminished output of heat. That a 

 lowering of general metabolism is attended by diminished 

 heat production is shown in the case of such diseases as 

 myxcedema and diabetes, in which the body temperature 

 is habitually subnormal ; and it is conceivable that in 

 some individuals an unusually large fraction of the 

 energy set free by oxidation of the food is converted to 

 work, and an unusually small fraction to heat. It must 

 be admitted, however, that investigations into the 

 metabolism of obese individuals have not clearly estab- 

 lished the occurrence of such physiological economy, 

 though some distinguished physiologists, such as Cohn- 

 heim and Bouchard, have been believers in its possi- 

 bility. Meanwhile the question must be regarded as 

 still sub judice. 



Individual variations in muscular tone must also, as 

 already described, affect the total amount of metabolism. 

 A * highly strung' person is one whose muscles are 

 always in a high state of 'tone,' and are therefore 

 always consuming energy ; such a one has brisk knee- 

 jerks, and is characterized by ' energy ' which leads him 

 to perform muscular movements very quickly (and 

 therefore uneconomically), and also to be constantly 



