UNIFORMITIES AND COMPAEISONS AMONG COMPONENTS 377 



(Dill et al., '38). The exchanges and velocity quotients are not, it 

 seems, permanently fixed when the load first appears; a sort of 

 conditioning is apparent, using that term either as an ecological or 

 a psychological one. Occasionally such progression with time is 

 termed adaptation, or accommodation; each term has its implica- 

 tions which no one wishes to extend to all phenomena in which 

 repetition has an effect. Here is evidence that patterns of main- 

 tenance are not all preformed ; it is possible that exchanges of many 

 components are changed with experience superimposed upon initial 

 endowment. 



In general, most components of organisms appear to be pro- 

 vided with outlets that pump faster in repletion, and with intakes 

 that pump faster in depletion. Each of many physiological func- 

 tions has flood controls and drought controls. Turnover is absent 

 for those components whose content is zero, and for relatively few 

 others. Where continuous turnover occurs, machinery for recov- 

 ery is already in motion ; recovery is achieved ' ' by modifying the 

 speed of a continuous process" (Cannon, '32, p. 181). 



§ 136. Velocity quotients 



Instead of regarding each component and its compensations as 

 discrete, I can next regard them as coexisting in one individual. I 

 can then compare the adjustments of diverse components, and not 

 merely in terms of what tissues handle them, but also quantita- 

 tively, and chiefly by means of velocity quotients. Velocity quo- 

 tients have the same dimensions as constants of chemical reactions, 

 and wherever they are constant with time, correspond to reactions 

 of the ''first order," whether or not chemical transformations are 

 involved. Their numerical values indicate how many times over, 

 a load of the given amount would be disposed of in one hour. 

 Diverse components in one species (table 40) of which the extreme 

 loads studied are less than the tolerated loads, show an enormous 

 range of values of this quotient. In man the extreme quotients 

 differ by a factor of 10^ ; more extreme quotients may be found in 

 still other components, as would be apparent if the recovery of 

 excitability in nerve (16,000,000/hr., <^ 128) were included in the 

 comparison. 



Grading components according to the velocity quotients shown 

 in their adjustment, I note (table 41) that respiratory exchanges 

 and heart frequency recover most rapidly. The elimination of 



