272 



SENESCENCE AND REJUVENESCENCE 



body is constant irrespective of age. Table V (Rubner, '85) gives 

 the rate of metabolism in man at different ages, measured in terms 

 of heat production in calories for periods of twenty-four hours, 

 and also the heat production per kilogram of body-weight and per 

 square meter of body-surface. 



TABLE V 



It is evident from this table that the heat production per square 

 meter of surface does show a considerable degree of constancy in 

 the individuals of different sizes and weights. In various other 

 papers Rubner has presented additional evidence for his view that 

 the rate of metabolism per unit of body-surface remains essentially 

 the same throughout life. According to Rubner then the rate of 

 metabolism is in some way regulated by the relative amount of 

 body-surface, i.e., the loss of heat determines the heat production, 

 and since the surface increases less rapidly than the volume or 

 weight of the body the rate of metabolism per unit of weight must 

 decrease, as the third column of Table V shows. 



This view has not found general acceptance. Not only has the 

 method of measuring body-surface been criticized, but it has been 

 pointed out that during later life in man the rate of metabolism 

 and therefore of heat production certainly decreases progressively 

 while the body-surface remains practically unaltered. According 

 to Magnus-Levy the minimum metabolism in old age may be as 

 low as 20 per cent of the normal, and various authors have shown 

 that the daily metabolic exchange also decreases. Hill has recently 

 shown also that the ratio of heat production to body-surface is not 

 constant in rats of different size. In small individuals it is as high 



