UNIFORMITIES AND COMPARISONS AMONG COMPONENTS 373 



as a fraction of the body's control content. But this is difficult to 

 accomplish for heat, temperatures, pressures, and electrical poten- 

 tials, which either have no physiological zero or are regularly 

 absent from the body. If fraction of control content could be used 

 universally, it would have the advantage that every conceivable 

 component, regardless of its physical dimensions, could be ex- 

 pressed in it. 



Loads might also be equated in units of variability (o) or in 

 units of daily or hourly differences (CA). This, the ''beta'^ 

 method, would have the advantage of being independent of all 

 physical dimensions, and the great disadvantage of requiring a 

 special study of variability before any comparisons could be made. 



Could lethal extremes be used to equate loads to a common 

 scale? The difficulties here are: (l) the physical scales would dif- 

 fer from the physiological scales within the range of positive loads 

 as compared with the range of negative loads; (2) the scales would 

 differ for two types of loading of the same component, one of which 

 killed at a less point on the physical scale; (5) no lethal load exists 

 for some components; (4) the scale of loads would be revised with 

 each statistical investigation of tolerated maximum; (5) in man 

 the lethal limit could often not be determined, and in elephants 

 would be rather expensive. On the whole, I see no probability of 

 finding a biological means of making commensurate loads of all 

 types and components. 



Loads from which recoveries occur evidently represent debts 

 and credits in the organism. For some, equivalents are known that 

 act as security for their discharge (phosphocreatine for oxygen, 

 hydrogen ions for carbon dioxide, osmotic pressure for water). It 

 is unnecessary to limit the measurement of debts and securities to 

 chemical or any other variety of components. The security may 

 be divided among many forms at one time. The combined states 

 and activities of the organism represent this security, as evinced 

 in everything that changes during recovery. 



§ 135. Rates of exchange 

 Rates of physiological activity are comparable for various com- 

 ponents wherever the components have similar dimensions or 

 known equivalences. Sometimes dimensions themselves can be 

 transformed with high assurance of accuracy, as in the loss of heat 

 (cal./kg. hr.) by evaporation of water {% of Bo/hr.), when the 

 latent heat of vaporization is believed to be known. 



