PERIODICITY IN HUMAN BEINGS AND MICE 835 



tration of two shocks at 8 a.m. and two at 8 p.m., for 10, 11, and 12 

 days, respectively). The results indicate a high degree of independence 

 of these rhythms, from the cerebral functions which are gravely al- 

 tered, if not obliterated, by R.E.S.T. In the periodogram, the value for 

 the trial period of about 12 hr was consistently lower than the peak 

 found at about 24 hr, despite the continuance of the 12 hourly shock 

 schedule for almost two weeks. As compared to other more physio- 

 logic studies on the possible adaptation of human beings (Kleitman 

 andKleitman, 1953; Lewis and Lobban, 1954, 1957a,b; Mills, 1951) 

 or experimental animals (Tribukait, 1954, 1956) to unusual sched- 

 ules, the R.E.S.T. results differ in the circumstance that R.E.S.T. may, 

 perhaps, be regarded as a drastic "stressor" (Selye, 1953, 1954, 

 1956). This stressor, applied at intervals of 12 hr, failed to imprint a 

 dominating 12-hr schedule upon certain 24-hr rhythms. That R.E.S.T. 

 should do so at all can be expected only by those who choose to regard 

 24-hr rhythms as direct reactions to the 24-hr schedule of the "stresses" 

 of daily life. This seems hardly a useful approach, since in doing so 

 one inadvertently ignores the organism's own integrated sequence of 

 24-hr periodic events. It seems pertinent that Selye, by contrast to 

 others, to our knowledge has refrained from usins; the not uncommon 

 "interpretation" of physiologic rhythms as "stress reactions" (i.e., as 

 exogenous effects unqualified as to endogenous circadian organiza- 

 tion). 



If during the first week of 12 hourly R.E.S.T., there was a transient 

 shortening of r (= average period for temperature or eosinophil varia- 

 tion in a given patient), this almost certainly did not exceed 1 hr or 

 so. It would appear that (1) physiologic periodicity represents a 

 mechanism that adapts to changes in schedule, as long as such 

 changes are, so to speak, within reason; (2) but that under the condi- 

 tions of 12 hourly shocks, the shortening or lengthening of its primary 

 period is slight, at most by a few hours rather than by 12 hrs; in other 

 words, certain schedules may not be acceptable, even though they are 

 forced upon the organism in a drastic fashion, such as R.E.S.T. 



Conceivably, certain 24-hr rhythms assume a free-running circadian 

 period in human beings as well as in the studies of Tribukait (1954, 

 1956) on the mouse, if they are continuously confronted with certain 

 environmental schedules which exceed the plasticity of metabolic 



