MELANOPHORES OF THE HORNED TOAD 305 



adrenal glands, removal of these bodies might be expected to 

 check the reaction. It is not difficult to open the body cavity 

 of a horned toad, tie ligatures about the membranes supporting 

 the adrenal glands, and cut out these bodies. It is necessary to 

 take with them the gonads and a portion of the genital ducts. 

 Although the operation involves tying off the postcava, other 

 veins are able to compensate for the loss of this vessel, and the 

 animals live for a week or more. It was stated in a preliminary 

 communication (Redfield, '16) that this operation does not 

 check the contraction of the melanophores by noxious stimuU. 

 This observation was based upon experiments upon only a few 

 animals. A larger series has since been operated upon and two 

 horned toads fomid which fulfilled the requirements of the hy- 

 pothesis. Although these animals became very pale in less than 

 four minutes when the mouth was stimulated by a weak f aradic 

 current of electricity, after the removal of the adrenal glands no 

 contraction of the melanophore pigment resulted, although the mouth 

 was stimulated in the same way for twenty minutes. The conclusion 

 is unavoidable that the hormone responsible for the original con- 

 traction of the melanophore pigment, as the result of noxious 

 stimuli, is produced by the adrenal glands. 



Turning to the larger number of animals in which removal of 

 the adrenal glands proved ineffective in checking the reaction, it 

 must be pointed out that in these horned toads the contraction 

 of the melanophore pigment was somewhat slower and the skin 

 never became as pale as before adrenalectomy. On page 308 an 

 experiment will be described which proves conclusively that this 

 incomplete reaction is due to the action of the nervous system 

 upon the melanophores and shows that when the nervous system 

 has been destroyed removal of the adrenal glands is necessary 

 before the reaction can be blocked. 



In the foregoing pages evidence has been presented indicating 

 that: 1) adrenin contracts the melanophore pigment of the 

 horned toad; 2) the adrenal glands contain this substance; 3) 

 stimulation o" these glands causes the melanophore pigment to 

 contract; 4) following noxious stimulation, adrenin occurs in the 

 circulation and the melanophore pigment contracts; 5) the 



