374 PHYSIOLOGICAL EEGULATIONS 



The recital of the rates of turnover of diverse components, as 

 in table 40, may be of interest in certain connections. Each mean 

 rate, and the variability of each rate, characterizes the individual 

 and the species. It establishes norms against which any unusual 

 individual or an individual in any new physiological state may be 

 compared, in much the manner that physical anthropology and 

 clinical medicine practice. 



It is not always realized that most components concerning 

 whose gains and losses little is known, still have turnovers. Con- 

 stant potential, pressure, or concentration probably represents 

 continual decay and replacement, though no prediction may be safe 

 for all components. Prothrombin in dog's plasma decays after the 

 plasma is isolated from the body ; in fact no organic compound in 

 wet killed tissue is known to last indefinitely. Often intermittency 

 of content furnishes a means of estimating turnover rates. Thus, 

 arterial blood pressure falls during each diastole ; this fall multi- 

 plied by the heart frequency, is the turnover of pressure. And so 

 minimal values of the turnover of excitability in heart, peristalsis 

 in gut, tension in single muscle fiber, and lift during walking are 

 ascertained. In general, measurements of turnover depend upon 

 one of the following methods: (a) flow across a boundary, (b) 

 difference in flows to and fro (arteriovenous differences), (c) 

 accumulation of marked materials, and (d) intermittent contents. 

 All methods treat the rate as though stationary over some period 

 of time. 



In the study of regulations of any one component the several 

 rates of exchange relative to turnover rates are indicated by aug- 

 mentation ratios and modification ratios ; they indicate the latitudes 

 over which rates of exchange respond. The maximal rates of ex- 

 change express capacities with which each organism is endowed. 

 In particular, it turns out that for most components (table 40) the 

 maximal rate of gain is similar to the maximal rate of loss. 



For a few components, economy quotients (ratio of total gain 

 to total loss) are known. At extreme loads it is the rule that econ- 

 omy quotients are far from 1. A ratio similar to the economy 

 quotient was proposed by Verworn (1898, p. 487), termed "bio- 

 tonus," representing the rate of assimilation or anabolism relative 

 to the rate of dissimilation or catabolism. Metabolic equilibrium 

 prevailed only when the ratio was 1. This limited form of econ- 



