866 PERIODIC FUNCTIONS IN MAMMALS 



6. Problems of physiologic "synchronization" then are depicted. 

 A crude and inadequate scheme of neural, endocrine, and metabolic 

 interactions involved in mammalian 24-hr periodicity is discussed. 



7. Twenty-four-hour periodic changes in physiologic state represent 

 an integrative as well as adaptive characteristic of the organism, rather 

 than merely "reactions" to factors from without. Some limits to the 

 adaptability of periodic body functions and the critical extent to 

 which the organism's periodicity determines its ability to withstand 

 damage were indicated. 



COMMENT 



Most of the data presented and discussed herein represent the work of 

 many individuals at the Cambridge State School and Hospital as well 

 as at the University of Minnesota Medical School (see References). 

 They constitute, of course, only a few selected aspects of much broader 

 problems (Aschoff, 1955, 1958; Bliss, 1958; Brown, 1957a,b; Cal- 

 houn, 1944; Everett and Sawyer, 1950; Geyer and Keibl, 1953; 

 Haus, 1957; Hechter, 1957; Hendricks, 1956; Isikawa, 1931; Man- 

 son-Bahr and Alcock, 1927; Menzel and Othlinghaus, 1948; Mlihle- 

 mann, 1956; Richter, 1956; Stephens, 1957; Strughold, 1952; Szego, 

 1957; Tatai and Osada, 1956; Toole et al, 1954; Withrow, this 

 volume). 



The electronic analogies in this paper emerged from long discussions 

 with Earl Bakken. They were used ( 1 ) in an attempt to predict what 

 the lighting schedule will do with respect to phase of mammalian 

 rhythms, while (2) we endeavored to achieve this prediction in ac- 

 cordance with the available pertinent anatomical and physiologic 

 information. If the analogies are useful in experimental design for 

 the first purpose, the credit is Mr. Bakken's, but if, as is certain, our 

 crude discussion of neural-endocrine-metabolic interactions will be 

 inadequate to achieve the second purpose, only the authors are 

 responsible for interpretations. It would appear, indeed, that physio- 

 logic periodicity analysis is a field replete with important data and with 

 stimulating concepts. But it awaits the design and the application of 

 appropriate methods for quantitative estimations of period, amplitude, 

 and phase of rhythms, at different levels of organization in many forms 



