358 PHYSIOLOGICAL, REGULATIONS 



During the course of a single recovery of electrical excitability, 

 the net rate of change is, according to Blair ( '36, p. 65), expressed 

 by the equation BQ/At = A:AQ, in which Q is the reciprocal of the 

 potential required to excite in the control state. This h is the 

 velocity quotient as defined above ; in frog nerve, as in many other 

 tissues, k is constant. For his frog nerve in conditions chosen, 

 the velocity quotient has the value 16,000,000/hour ; half -life 

 = 0.45 milliseconds. With other electrodes and other conditions, 

 h would be somewhat different. On the whole, these are recov- 

 eries that occur at enormously faster rates than any mentioned 

 above. 



By another method it is possible to produce varying initial 

 deficits of excitability. At one locality of the isolated nerve first an 

 inadequate stimulus is given, followed at a stated interval by one 

 now just adequate to gauge the excitability of that locality. In that 

 manner only the first portions of recovery are evaluated, as was 

 done for many other components. 



Much of the special descriptions given to excitability, and to 

 recovery from it, may be recognized as particular forms of relations 

 that are as general as equilibration itself. Whether the special 

 features are more than quantitatively different from other main- 

 tenance remains, I think, to be ascertained. 



§ 129. Other data 



Numerous materials are available for the quantitative study of 

 recovery processes, though none seem to be recorded exhaustively. 

 I imagine there is no need to exhibit further examples in detail. But 

 I have examined a sufficient number to give me the impression that 

 a great portion of quantitative physiology could be represented in 

 the form of equilibration diagrams and tolerance curves. 



Some additions to the repertoire already exhibited, which I have 

 visualized to date, are : 



(1) Clearances, whether of plasma, blood, or other tissue; 

 whether renal, hepatic, or in any other path; whether labelled as 

 such or not. In each case a rate of loss (disposal) or of gain 

 (accretion) is correlated with a concentration present. Many 

 clearances in dog and in man are reviewed by H. W. Smith ('37). 

 Other ''disappearance curves" are for dyes (H. P. Smith, '25), 

 galactose (Bollman et al., '35), borate (Rost, '03; Michaelis and 

 Maass, '07), ethyl alcohol (Ewing, '40), propylene glycol (New- 



