156 Ri( HARD M. F'rai'S 



gestagens (69). While such compounds have not been demonstrated in the 

 blood of hens, it seems not improbable that the Hooker-Forbes test measures 

 "the circulating form or forms of the luteal hormone" (12) in the hen 

 as in other species. It is of some interest in this connection that Lytle and 

 Lorenz (41), referring to earlier work by Lytle, state that chemical analysis 

 failed to identify progesterone in blood drawn by heart puncture, although 

 this blood yielded positive responses by the Hooker-Forbes test. Lytle and 

 Lorenz note also that relatively large samples, drawn to circumvent loss in 

 peripheral tissues but less completely defatted than were their definitive 

 samples, uniformly failed in chemical tests to yield measurable quantities of 

 progesterone while eliciting positive responses in the Hooker-Forbes bioassay. 



The demonstration that progesterone is formed in the hen's ovary, is 

 secreted as progesterone into the systemic blood, and is associated with 

 progestogenic activity as measured by the Hooker-Forbes test, would appear 

 to support the conclusion that the naturally occurring "excitation" hormone 

 is a progestagen if not progesterone itself. 



The stimulus for the postulated formation of progesterone in the maturing 

 follicle must remain a matter of conjecture. It seems possible that the same 

 gonadotropin release causing ovulation of the mature follicle may initiate in 

 the succeeding follicle the processes leading to the elaboration of progesterone. 

 Theoretically, at least, prolactin may be involved in the maintenance of 

 progesterone production, or the "basal level" of LH may be a factor. The 

 subject obviously calls for more attention than has been accorded it in the past. 



A not unrelated question concerns possible functions of the hen's ruptured 

 ovarian follicle which, as van Tienhoven (65) has recently emphasized again, 

 is not to be confused with the mammalian corpus luteum. The ruptured 

 follicle is essential for oviposition (57), and it contains progesterone (39). 

 Practically nothing else seems to be known about the structure. Its rapid 

 resorption following ovulation need not exclude some important short-term 

 role in the cycle, but one could only speculate on what this might be. 



The Nalbandov Hypotheses 



Two explanations of the ovulation cycle have been developed by 

 Nalbandov (42, 44). Both stem from the results of experiments, described 

 earlier, demonstrating the suppression of LH release for ovulation, but not 

 of other gonadotropic-dependent functions, by irritants in the magnum or 

 isthmus of the oviduct (35, 63). In accounting for their observations, Huston 

 and Nalbandov (35) postulated that the pituitary of the ovulating hen secretes 

 FSH and LH at a continuing and relatively steady basal level; periodically, 

 LH is released in greater quantities to effect ovulation. The oviducal irritant 

 was believed to suppress, over neurogenic pathways, only the periodic LH 

 releases required for ovulation. These authors, and Nalbandov (42), con- 

 sidered also the possibility that the presence of an egg in the magnum might 



