306 ALFRED C. REDFIELD 



melanophore pigment is contracted at other times when he 

 presence of adrenin in the circulation is to be expected, and 6) 

 the removal of the adrenal gland hinders or prevents the contrac- 

 tion of the melanophore pigment by noxious stimuli. In view of 

 these facts, it must be concluded that the hormone which causes 

 the melanophore pigment of the horned toad to contract during 

 states of nervous excitement is adrenin, the active principle of the 

 adrenal glands. 



2. Coordinative action of the nervous system 



a. The nervous control of melanophores. Any experiments 

 designed to demonstrate the innervation of pigment cells are 

 invalid unless care is taken to eliminate the action of hormones 

 upon the part of the body under examination. The production 

 of adrenin in response to noxious stimuli presents a real difficulty 

 in such an investigation because the operative procedure in- 

 volved in cutting and stimulating nerves is quite sufficient to 

 produce a contraction of all the melanophore pigment through the 

 action of this hormone. This difficulty has been overcome by 

 destrojdng the anterior part of the spinal cord of the horned toad 

 to be experimented upon. When this is done the animals 

 recover completely, but no longer respond to noxious stimuli 

 by contracting the melanophore pigment. Apparently the 

 operation destroys the 'center' or the tracts of efferent nerve 

 fibers which activate the adrenal glands. The operation has the 

 additional advantage of allowing one subsequently to operate on 

 the posterior part of the body without the use of anaesthetics. 



The following experiment shows the effect of stimulating the 

 spinal and sciatic nerves of horned toads prepared in this manner : 



August. 11, 1915. Etherized two horned toads and removed the 

 spinal cord between approximately the eighth and the thirteenth 

 vertebrae. 



August 12, 1915. Skin of right side of back of one of these animals 

 was cut open and a spinal nerve (the twelfth?) dissected out and stim- 

 ulated with a weak faradic current for ten minutes. Produced abso- 

 lutely no change in the melanophores of any part of the skin. 



Stimulated the sciatic nerve of the left hind leg of the other animal 

 for five minutes with a weak induction current. Produced a very 



