824 PERIODIC FUNCTIONS IN MAMMALS 



in pouch and pinnal epithelium of the hamster (Chaudhry et ah, 

 1958). Thus, on one hand, we may postulate for mitotic rhythms in 

 several tissues and in different species, the operation of systemic con- 

 trolling mechanisms (which are of obvious interest to the student of 

 cancer). On the other hand, in the mouse, the mitotic rhythm of 

 adrenal parenchyma exhibits important phase differences as compared 

 to the rhythms in liver parenchyma or skin epidermis. This finding, in 

 turn, may be used to suggest that the "night-watchman," the adrenal, 

 assumes a schedule which is quite different from that of tissues, the 

 activity of which it guards. Moreover, in speaking thus of activity we 

 may not have to restrict ourselves to mitotic behavior in the adrenal 

 and elsewhere but, perhaps, we may also draw inferences from the 

 mitotic behavior of a given tissue to its "functional" activity along the 

 24-hr scale. In this connection, it is pertinent that Peter (1940), 

 among others, has suggested that the factors which regulate mitosis 

 vary inversely with the function of an organ. In the thorough and ex- 

 tensive studies of Blumenfeld (1942), mitotic activity in the renal 

 cortex was minimal at the time of maximal urinary excretion and 

 maximal at the time of minimal urinary excretion. In the submaxillary 

 gland, the same author has found an inverse relationship between the 

 rates of mitotic activity and of functional activity in association with 

 food intake. In view of the foregoing evidence, the basic processes of 

 a cell were divided by Blumenfeld into functional and vegetative ac- 

 tivities. One state ceases when the other begins; cells undergo divi- 

 sion during the vegetative state, upon cessation of the functional state. 

 With this background of thought, it seemed desirable, of course, to 

 deal more specifically with those cellular processes which characterize 

 in biochemical terms the alternating states of "functional" and "vegeta- 

 tive" activity. We set out in Minnesota to undertake this task of "re- 

 solving" cellular events in metabolism along the 24-hr scale. For our 

 first studies we chose mouse liver and a "whole-animal" approach. The 

 simple assumption underlying our work was as follows: if cellular 

 functions normally exhibit 24-hr changes in rate, periodicity analysis 

 ought to reveal important differences in phase of rhythms, for those 

 functions that are dissociated in time (e.g., "functional" versus "vege- 

 tative" ) . The results obtained for a few variables were studied by the 

 combination of several techniques, namely of periodicity analysis 



