PERIODICITY IN HUMAN BEINGS AND MICE 



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Fig. 8. Corroboration of impression with respect to possible phase 

 differences in eosinophil rhythm of blinded and sham operated animals. 

 Temporary antiphase brought about by operation of circadian periods. 



the environmental day. Circadian periods that may be slightly yet 

 significantly different from 24 hr can thus come to the fore. The signi- 

 ficance of such periods, e.g., of 23 hr and 20 min duration, for our in- 

 terpretation of rhythms lies in the fact that we know of no environ- 

 mental periods of corresponding lengths and consequently we can as- 

 sume that they are self-determined from within the organism, rather 

 than forced upon it from without. Those circadian periods that are 

 significantly different from 24 hr also constitute the major method- 

 ologic pitfalls for those who want to "control" daily rhythms by sam- 

 pling always at the same time of day in an endeavor to obtain compa- 

 rable data; actually, by such a procedure one makes certain to sample 

 at different physiologic times, as soon as free-running periods prevail. 

 Among mammalian functions other than motor activity, we have 

 studied more extensively the dissociation of rectal temperature 

 rhythm from the environmental time scale, e.g., after blinding of 



