2. Endocrines and Populations 217 



Plainly there are many problems still to be solved before a complete and 



detailed explanation of the regulation of the release of ACTH and the 

 fascicular corticoids will be possible, but the evidence for the mechanisms 

 which have been described is strong. There is no doubt that the hypothala- 

 mus has a major role in the regulation of ACTH release and of adenohy- 

 pophyseal function in general, and there is no reason to question the 

 existence of such a neurohumoral mechanism. The evidence for some of the 

 details, however, is less conclusive. The cortical glomerulosa and the re- 

 lease of aldosterone are largely independent of this system of regulation, as 

 indicated earlier, except for a very moderate response to ACTH for a 

 limited time. 



c. The junction of the zona reticularis. The zona reticularis has been 

 thought to secrete sex steroids (Selye, 1947), especially androgens, but 

 the evidence for such a function is poor and largely inferential (Dempsey, 

 1948; Creep and Deane, 1949b; Jones, 1957). This zone is made up of a 

 continuation of the cords or continuum, as the case may be, of the zona 

 fasciculata, the cells of which are in varying degrees of activity and respond 

 accordingly to stimulation by ACTH (Jones, 1957). By and large they 

 have the appearance of cells of the fasciculata which are declinmg in ac- 

 tivity and becoming obsolete, but there is certainly some functional capa- 

 city in the reticular cells, as indicated by various histochemical procedures 

 and the presence of mitosis, although it is apparently much less than that 

 of the zona fasciculata (Dempsey, 1948; Creep and Deane, 1949b) . Syming- 

 ton et al. (1958) have presented convincing morphologic and histochemical 

 evidence, coupled with secretory studies, that the reticularis normally 

 secretes the hormones usually attributed to the zona fasciculata and that 

 the latter is in a resting state until fvnther stimulated by ACTH. This sug- 

 gestion is well worth considering especially as morphologic changes are 

 related to steroid production by direct measurement. These studies necessi- 

 tate a revision of the classic concepts of the functional roles of the reticularis 

 and fasciculata which have been based only on morphologic evidence. 



d. The problem of the function of X-zone. The X-zone of the adrenal cortex 

 of the immature house mouse (Mus musculus) is maintained by gonado- 

 tropin rather than by ACTH or growth hormone (Jones, 1949b, 1950, 1952, 

 1957) . Its function is unknown, and histochemically it does not present the 

 appearance of being a secretory zone (McPhail, 1944; Howard, 1939; 1946; 

 McPhail and Read, 1942a, b) . The cells do not give the usual histochemical 

 reactions for steroids or other lipids, although they do contain ascorbic 

 acid (Jones, 1949a, 1950) . There is no evidence that the X-zone of the 

 house mouse secretes sex steroids (McPhail, 1944; Jones, 1957), although 

 such a function has been postulated by several investigators (Jones, 1957) . 

 In fact the large amounts of Cig steroids secreted by the adrenals of mice in 



