THE PITUITARY BODY 



third ventricle of the frog was soon followed by a dispersion 

 of the melanosomes. This change was not prevented by 

 transection of the spinal cord in the cervical region. From his 

 experiments Zieske (1932) concluded that secretory fibers 

 probably pass down the "stalk" and, after entering the neuro- 

 intermediate lobe, terminate in the lateral portions of the 

 pars intermedia. He found that, after the division of the 

 neuro-intermediate lobe in the mid-line, the frogs {Hyla 

 arbored) remained dark or black, whereas if similar incisions 

 were made on either side of the mid-line, the coloration of 

 the frogs changed from black to green. 



If frogs are kept in complete darkness for about 20 minutes, 

 the melanosomes become concentrated and the hormone 

 causing their dispersion is said almost to disappear. On the 

 other hand, exposure to light for as short a time as 15 

 seconds causes the reappearance of the hormone because of 

 optic stimuli. The effective stimuli arise from the blue end 

 of the spectrum; red or yellow light is much less effective 

 (Koller and Rodewald, 1933). Rodewald (1935) later made 

 a further study of these and related phenomena; however, un- 

 like Jores (1934), she did not find that alkaline extraction of 

 the pituitary of frogs kept in darkness "reactivated" the 

 pituitary. 



According to Dietel (1933), the melanosome-dispersing 

 hormone causes a capillary dilatation in the frog. 



The effects of an extract of the pars intermedia (ox) on 

 the appearance of a normal frog is illustrated in Figure 52. 

 Photomicrographs showing the cutaneous melanophores be- 

 fore and after the injection of the extract are reproduced in 

 Figure k,-;}^. Hogben and Winton (1922 and later) as well as 

 numerous other investigators have studied the effect of ex- 

 tracts on the melanophores of intact and hypophysectomized 

 frogs and toads as well as on the isolated skin of the frog. 

 Most of these reports are referred to later. However, ex- 



