INTRODUCTION 9 



part of the pituitary gland was implanted in them. The 

 blanching of the common frog after the removal of its 

 pituitary gland was incidentally recorded by Krogh in 

 1922. Meanwhile Hogben and Winton had been ac- 

 tively engaged in experiments on the color changes of 

 frogs in relation to nerves and the pituitary secretion. 

 Their papers, which appeared in 1922 and 1923 and were 

 based chiefly on a study of the European frogs, led to 

 rather startling conclusions. In these it was pointed 

 out that nerves played a wholly insignificant part in the 

 control of color changes in amphibians, if, in fact, they 

 had any part at all. The dark phase of the frog was 

 shown to depend upon a secretion derived from the 

 pituitary gland, probably from its intermediate part. 

 This secretion was carried from the gland by the blood 

 to the melanophores, whose pigment was thereby in- 

 duced to disperse. The pale phase of the animal was 

 not so consistently worked out. In the early steps in 

 his work Hogben appears to have entertained the view 

 that this single neurohumor, the intermediate-pituitary 

 secretion, was all that was involved in the frog's change 

 of color. This secretion when present in the fluids about 

 the melanophores called forth the dark reaction, and its 

 absence from these fluids allowed the pale phase to inter- 

 vene. Subsequently Hogben and his associates worked 

 upon other species of frogs and particularly upon the 

 South African toad, Xenopus. As a result of these later 

 investigations he and Slome became persuaded that at 

 least in the amphibians just named there was evidence 

 for a second humor which, though derived from the 

 pituitary complex, nevertheless induced a concentration 

 of melanophore pigment (Slome and Hogben, 1928, 

 1929; Hogben and Slome, 1931). This humor, though 

 a product of the pituitary gland, was thus the counter- 

 part of the first one. These investigations were pub- 



