The physiological rhythms of subjects living on a day of abnormal length.

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Abstract
Subjects (14), singly or in groups, were observed while living on a 21 h day for 8 or 16 experimental days and 15 other subjects similarly on a 27 h day. Rhythmic components of body temperature and excretion of various urinary constituents were calculated. On a 21 h day, for most components and most subjects, 2 periods were present, 1 of 21 h and 1 of of 24 h. On a 27 h day 2 periods were less often present and a larger number of observed rhythms could be satisfactorily described by a single period, usually between 23-28 h. In subjects spending a 2nd wk on a 21 h day the circadian component was no less prominent than during the 1st wk. When, after life on a 21 h day, subjects were deprived of knowledge of time, there was evidence that the 21 h component did not persist. The results are interpreted as evidence of the continuing existence of an influence with a period of around 24 h, simultaneously with rhythmic influences resulting from the subjects'' habits. On a 27 h day there was sometimes evidence of entrainment, yielding an intermediate period. An attempt is made to compare the relative potency of the exogenous and the persistent circadian influences on the several variables.