104 



KINETIC HORMONES — I 



If the posterior lobe of the pituitary is removed (taking with it 

 the pars intermedia, which is the source of B, while the pars 

 tuberalis is left intact) a similar dose of B results in the least and 

 shortest response of the three (Fig. 3-22, curve C). If there were no 



V: Total removal 



8 10 12 



Hours 



18 20 



Fig. 3-22. Effects upon the melanophores of Xenopus of extracts, 

 containing equal amounts of the melanin dispersing hormone, B 

 (intermedin). (A) Six toads from which the whole hypophysis, 

 including sources of both B and W, has been removed. (B) Six 

 normal intact toads, in which production of both hormones is 

 stimulated by the white background. (C) Six toads from which the 

 posterior lobe and the pars intermedia have been removed, taking 

 with them the source of B only. For further explanation see text. 

 B was obtained from extracts of ox ''posterior pituitary", freed 

 from pressor and oxytocic activity, but including intermedin from 

 the pars intermedia to provide a dispersing effect. Although this 

 is not the natural amphibian hormone, the facts of the dose being 

 the same in each case and producing slow dispersion, and the fact 

 that the magnitude of the effect is altered by prior operations on 

 the toads make the results appear significant. The specimens used 

 for the experiments were "selected for the same degree of pallor", 

 and all were exposed to an illuminated white background (from 

 Hogben and Slome, 1936). 



active hormone secreted by the pars tuberalis, this curve should 

 be the same as curve Ay since the source of B is absent in both 



