300 ALFRED C. REDFIELD 



during functional activity, produce enough of this hormone to 

 cause a contraction of the melanophore pigment in the skin? 



A difficulty arises in attempting to discover the answer to this 

 question. In order to stimulate the adrenal glands, the body 

 cavity must be opened. If the animal is etherized before per- 

 forming this operation, the melanophore pigment contracts and 

 renders the continuance of the experiment futile. If eitheriza- 

 tion were omitted, the operation of itself would constitute a 

 noxious stimulus and produce a contraction of the pigment. 

 Fortunately, it has been discovered that the destruction of the 

 spinal cord between the eighth and thirteenth vertebra prevents 

 the contraction of the melanophore pigment which normally 

 follows noxious stimulation. After operating on horned toads in 

 this way, it is possible to open the body cavity without causing 

 the melanophore pigment to contract. The use of anaesthetics is 

 rendered unnecessary because the destruction of the cord pre- 

 vents the passage of nervous impulses from the posterior portion 

 of the body to the brain. 



If the adrenal glands of such a preparation be stimulated 

 directly by a weak faradic current, a complete contraction of the 

 melanophore pigment will occur in a few minutes. That this 

 result is not due to a nervous reflex is shown by the fact that if a 

 ligature is tied about one of the hind legs before the stimulation is 

 commenced, the leg will remain in its original dark condition after 

 the rest of the body has become pale (fig. 13). Upon removing 

 the ligature, the leg will become as pale as its mate, though stimu- 

 lation has ceased several minutes before. 



If a ligature is tied about the blood-vessels which supply the 

 adrenal gland, no change in the condition of the pigment cells 

 can be detected upon stimulating the adrenal gland until after 

 this ligature is removed. 



From these experiments it becomes quite clear that the adrenal 

 glands of the horned toad can produce a hormone when they are 

 brought into functional activity which contracts the melanophore 

 pigment. The coloration produced in this way resembles in 

 every respect that occurring during nervous excitement. 



