PERIODICITY IN HUMAN BEINGS AND MICE 845 



bears, jackals, wild and domestic dogs and dingos to cats, rabbits, 

 guinea pigs, hedgehogs, rats, mice, cocks, and owls, and she collected 

 data that showed the dependence of phase of rhythms investigated 

 upon external factors. 



Against that background and after many valuable studies by others 

 (Aschoff, 1958), the pertinent resuhs of Minnesota work were 

 gathered with the following aims in mind: first, to study in one ap- 

 propriate mammal, the mouse, the degree of generality of those 

 effects brought about by reversing the lighting regimen. Certain 

 physical, chemical, and morphological parameters previously found 

 to be periodic under physiologic conditions by others and/or ourselves 

 were chosen for this purpose from various levels of physiologic organi- 

 zation. A pathological periodicity that in convulsions, long known in 

 the clinic (Beau, 1836; Janz, 1955), for which we had devised, how- 

 ever, an experimental animal model (Halberg, Bittner, Gully, Al- 

 brecht, and Brackney, 1955; Halberg, Bittner, and Gully, 1955; Hal- 

 berg, Halberg, and Bittner, 1955) also was included for study. Second, 

 we were interested in possible differences in the effects of the lighting 

 schedule upon these various rhythms in the mouse. Third, we wanted 

 to see whether effects similar to those obtained in the mouse by chang- 

 ing the timing of the daily alternating light and dark periods also 

 may be obtained by changes in routine in human beings, and to 

 evaluate the statistical significance of these changes on groups of 

 volunteers when feasible. Thus we aimed, finally, at a species com- 

 parison, since some of those rhythms studied in mice were chosen for 

 human investigation as well. 



Let us now turn to results of an exploration of lighting effects at 

 lower levels of physiologic organization (Halberg, Barnum, Silber, 

 and Bittner, 1958). Again, two schedules of illumination were used: 

 the "regular" schedule provided for hght from 6 a.m. to 6 p.m., while 

 the "reversed" schedule provided for light from 6 p.m. to 6 a.m. All 

 the mice in each study were first kept on the regular schedule for a 

 week (for standardization). Thereafter, in the studies of blood glucose 

 (Fig. 19), liver glycogen (Fig. 20), and phospholipid (Fig. 21): (1) 

 the regular schedule was continued for some of the mice and replaced 

 by the reversed schedule for others; (2) either schedule was then 

 maintained unchanged for at least 2 weeks; and (3) the mice on 



