270 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the side of an aniaial on which the injection is made always remains 

 green longer than the opposite side. Since the nicotine does not act 

 directly upon the melauoi^hores, I believe this condition can be ex[)lained 

 only on the assumption of a stronger poisoning effect on the sympatlieiic 

 of the o^jera'ed side than on the other. This is the oidy piece of evi- 

 dence I have on the local action of the drug, but so far as it goes it 

 indicates that, as in mammals, local action of the sympathetic would be 

 followed by local reponse in the skin. 



In none of my experiments have I seen the least evidence that light 

 has any direct influence on the melanophores on entering or passing out 

 of the brown state. If a piece of brown skin is cut off from an animal 

 and quickly divided in two, one piece being put in the dark, and the other 

 exposed to daylight, both turn green at the same rate, and apparently 

 irrespective of the light. Many experiments of this kind have been 

 tried, but without the least evidence of the direct action of light on the 

 melanophores. 



The change to the brown state is thus not influenced by the direct 

 action of light. It may be brought about in at least two ways : first, 

 through the direct stimulation of the melanophores by such mechanical 

 means as tapping ; and, secondly, through the indirect action of light, 

 which stimulates the nerve terminals in the skin, and thereby induces 

 through the sympathetic fibres an outward migration of the melanophore 

 pigment. 



3. Green Condition. — The change from brown to green, as has 

 already been stated, invariably takes place when an animal is put into 

 the dark, and requires on an average twenty-five minutes for its comple- 

 tion. Since the dark is due to the absence of the stimulus, light, and is 

 not a stimulus itself, it would seem probable that the condition brought on 

 in the dark corresponds to the unstimulated or resting state of the cell. 



Much evidence has been obtained favoring this view, but before this 

 is presented, a word must be said about two ways by which the green 

 state may be brought about. As already noted, any means of stopping 

 the circulation will invariably induce the green state in the portion of 

 the skin affected. Thus, when a ligature is tied around the leg of an 

 animal, so as to stop the flow of the blood, the leg soon becomes green. 

 Since the animal reacts when the leg is touched, and moves the leg almost 

 normally in locomotion, it cannot be said thattlie ligature has temporarily 

 incapacitated the nerves. Wlien the ligature is removed, the leg cjuickly 

 becomes brown. The green condition, then, may be produced by cutting 

 off the blood supply. 



