PERIODICITY IN HUMAN BEINGS AND MICE 841 



higher centers is channeled, of course, neurally to the periphery, but 

 in addition, some of it also travels from the hypothalamus to the 

 pituitary (Fortier, 1951; Sayers et al, 1958). We are not certain 

 whether or not in the pituitary messages from above again are 

 compared with hormonal feedbacks from target glands (Sayers et al., 

 1958), but we can assume that in the case of altered phase relations 

 of CEPI and COPI the pituitary does send appropriate messages to 

 the "generators" of rhythms, until the alteration of phase is corrected 

 (Ingle, 1951b). The "messengers" are the pituitary tropic hormones; 

 the "generators" of rhythms appear to be (at first) the appropriate 

 target glands (see later for qualification); the latter are stimulated by 

 their tropins to speed up or they are slowed down by throttling of 

 tropin secretion until normal phase relations are reestablished. The 

 question may be raised, however, whether the path from the central 

 nervous system via the pituitary is obligatory for the transmission of 

 phase information to the target glands. This need not be the case in 

 all instances (Royce and Sayers, 1958). Of interest in this connection 

 is ample direct evidence as well as indirect evidence (Farrell et al., 

 1954; Liddle et al, 1955, 1956; Rauschkolb, 1956; Rauschkolb and 

 Farrell, 1956; Thorn, Renold, and Winegrad, 1957; Thorn, Ross, 

 Crabbe, and Hoff, 1957; Zimmermann and Schoenbauer, 1952) of 

 continued aldosterone secretion by the adrenal cortex in the absence 

 of pituitary function, and particularly the clinical work of Miiller et al. 

 (1958). Whether or not, under such circumstances, aldosterone 

 secretion is periodic, will have to be reinvestigated with more fre- 

 quent sampling along the 24-hr scale, a problem which remains 

 difficult in view of the exigencies of method. 



Two endocrines, the adrenal cortex and the female gonad can safely 

 be regarded as periodic glands par excellence, yet we can think of 

 other endocrine periodicity as well. For the case of the thyroid, the 

 existence of a characteristic period may not be unequivocally estab- 

 lished, yet the participation of this gland in the control, e.g., of 

 seasonal periodicity seems fascinating (cf. data of W. H. Brown, 

 1930). The same gland contributes, of course, to the maintenance of 

 24-hr rhythms, even though its effect may be exerted indirectly, via 

 classic thyroid-adrenal cortical interrelations. It seems pertinent that 

 periodic endogenous eosinopenia was not detected in thyroid insufii- 



