PERIODICITY IN HUMAN BEINGS AND MICE 849 



this study, the group on the regular schedule was sampled first. For 

 the remainder of the mice, the reversed schedule was then instituted 

 and maintained for 2 weeks prior to killing. Moreover, for the study 

 of corticosterone, pools of serum were used, by contrast to the rest 

 of the data, all of which describe individual mice. 



There was considerable variability in individual values and it also 

 is recognized that with such spot checks (at only two time points, on 

 the reversed schedule) the completeness of inversion of rhythm can- 

 not be ascertained, a consideration which seems particularly pertinent 

 to the data on hepatic mitoses (Figs. 22 and 25). We can conclude, 

 however, for all the functions studied, that an important shift of 

 rhythm had taken place after the shift of lighting schedule. Except for 

 blood corticosterone and some data in Fig. 25 (see below), the day- 

 night differences on both schedules were significant. Blood corti- 

 costerone is the only variable for which a statistical test was not 



8 days after reversal of I ightmg regimen { light from I8!00 to.06'.00) 

 t =2.79; P= .005 



-K^ 



Live r Parenchyma 

 (per 100 oil immersion fields) 



Skin" 



Cortex 



;per 3000 nuclei) 



Fig. 25. Data suggesting unequal shift times for phase changes of mitotic 

 rhythms in different tissues in mouse (see text). 



