PERIODICITY IN HUMAN BEINGS AND MICE 865 



the adrenal cortical and metabolic "arousals" ordinarily precede in 

 time cerebral cortical arousal. 



Can the altered phase relations of these "arousals" result in func- 

 tional impairment? Moreover, if left uncorrected, can such an impair- 

 ment of synchronization underlie disease? These are interesting clinical 

 problems, but their discussion is beyond the scope of this Symposium. 

 Here we have to note only that, at present, periodicity analysis for 

 clinical purposes represents no more than a potential tool, awaiting 

 rigorous tests of its usefulness. But in more basic fields related to 

 medicine, the method has proved itself in several instances as a 

 workable approach to at least one aspect of the critical problem of 

 physiologic changes with time. 



SUMMARY 



1. The desirability and feasibility of obtaining quantitative descrip- 

 tions of physiologic 24-hr periodicity by sample estimates of period 

 and amplitude have been illustrated. 



2. Free-running circadian periods (periods that may be slightly 

 but significantly difi'erent from 24-hr) have been explored at several 

 levels of physiologic organization in mammals. 



3. Several observations of 24-hr rhythms made under conditions 

 standardized for periodicity analysis in the mammal have been dis- 

 closed, and several other rhythms earlier described by others have 

 been reexamined under the same conditions. Maps "in time" for 24-hr 

 periodic physiologic changes thus were obtained. Such maps describe 

 a sequential order in time among physiologic events at several levels 

 of organization; they refer to normal and pathologic variables and 

 extend from the organism as a whole to certain aspects of nuclear or 

 cytoplasmic functions. 



4. Some factors from within the organism which underlie the 

 normal period of mammalian 24-hr rhythms, such as the adrenal cycle 

 and a metabolic sequence of cellular events are discussed. 



5. The effect of factors from without the organism, such as the 

 lighting schedule and/or the daily routine, was then illustrated in the 

 case of man and mouse; a species difference in the timing of rhythms 

 is documented. 



