826 PERIODIC FUNCTIONS IN MAMMALS 



of "dissimilatory" and "assimilatory" phases — useful first approxima- 

 tions), in the case of mouse liver, we may now refer to at least three 

 metabolic stages, each of ^8 hr duration. A first period. A, is marked 

 off by the peaks of mitosis and phospholipid; during the latter part of 



A, daily motor activity of mice is being initiated. The second period, 



B, between the peaks of phospholipid (or RNA) and DNA, represents 

 an "active" motor period of the mouse as a whole. The third period, 



C, between the peaks of DNA and mitosis, may be regarded as pre- 

 paratory for growth and repair; C can be subdivided, in turn, into two 

 subperiods, one preceding the glycogen peak (Ci) and the other fol- 

 lowing it (C2). Is C2 the "vegetative" state par excellence? The ques- 

 tion poses itself, whether an undisturbed C2 may not constitute an im- 

 portant condition for truly "recuperative" rest. By allowing for the 

 species differences in the phase of various mammalian rhythms (which 

 we shall bring to the fore later), we may further raise the question 

 whether the advantages of an undisturbed C2 may provide a metabolic 

 basis for the claim that homo sapiens, adapted to a diurnal schedule, 

 rests more "beneficially" during the early hours of the night than there- 

 after. At the present state of our knowledge on human metabolic 

 periodicity such considerations remain hypothetical. In the mouse, 

 however, it can be shown that our choice of the "right timing" may be 

 just as important for obtaining a given cellular effect as are our choices 

 of the "right hormone" and the "right dose" (Fig. 15) (Litman et al, 

 1958). 



The first period. A, between the peaks of mitosis and phospholipid 

 describes, perhaps, the metabolic preparation for daily motor (and 

 other?) activity. It is probably during A, that the adrenal cortex inter- 

 acts periodically with cellular metabolism in immature mouse liver and 

 perhaps in some other tissues as well. Information is available at least 

 with respect to the chemical nature of the adrenal hormone involved, 

 even though the pertinent data were obtained with an oxycorticoid 

 which is not the principal such corticoid of the species studied. With 

 this qualifying restriction, i.e., that cortisone (instead of corticoster- 

 one) was studied, it seems interesting that this 1 1 -oxycorticoid raises 

 the RSA of phospholipid phosphorus in liver cytoplasm of adrenalec- 

 tomized mice from levels, which are clearly below the physiologic 

 range, to values that appear to be within that range. More important. 



