368 PHYSIOLOGICAL REGULATIONS 



agents and conditions do to the organism and of what the organism 

 does in response. Partial generalized treatments of state II were 

 given by Widmark and Tandberg ('24) and Burton ('39). 



State III may not appear in a given instance, for the agents or 

 conditions that induced a load may be removed before it appears. 

 Constancy of load means that rate of gain remains equal to rate 

 of loss, and often state III is identified from rates of exchange. 

 Otherwise the stationary character may be judged solely from the 

 constancy of content. 



State IV is the portion of the sequence that has been studied 

 most extensively in this investigation. It seems to represent most 

 often what the organism does to adjust contents. Sometimes its 

 slopes are the reverse of those in state II. Very often the agents 

 that induced the load persist with diminishing effects for long 

 periods of time (as when drugs wear off or atmospheres gradually 

 cool), in which case recovery can hardly be regarded as an unen- 

 cumbered activity of the organism. Sometimes there is no way of 

 knowing how long agents persist (as when epinephrine is injected), 

 any more than of knowing exactly when agents not followed by 

 immediate consequences have become effective (as when water is 

 ingested). In all instances the investigator may choose a time that 

 can be recognized reproducibly and count hours from it, leaving to 

 anyone the "interpretation" of intervening events. 



State V is sometimes known only as an asymptote ; sometimes 

 it is assumed to be identical with the zero load of state I; some- 

 times it is acknowledged or demonstrated to be different from 

 state I. 



Very many physiological sequences are incomplete approaches 

 to hundreds of successive stationary states ; these may be regarded 

 as states Illd, Vc, etc., perhaps being distinguished only by 

 whether the load has just increased (III) or decreased (V). Thus, 

 an increment of blood volume, or a load rate of oxygen consumption 

 in a gastrocnemius muscle (Keller et al., '30) varies enormously 

 during each muscular contraction. Transitions and recoveries 

 probably succeed one another with each posture and each move- 

 ment ; and an asymptotic state is rarely reached. Data illustrating 

 the loads and rates involved during transitions from one stationary 

 state to another have been worked out with respect to rate of oxy- 

 gen consumption in human exercise (Hansen, '34; Szwejkowska, 



