174 JOHN N. LOWE 



The explanation for the localized areas of contracted pigment 

 cells may depend upon the selective action of morphine upon the 

 nervous system. 



The foregoing experiments support the conclusion that the 

 pigment cells are controlled by the medulla or the spinal cord. 

 It is probable that the localized areas of expanded and contracted 

 pigment cells are in direct response to the mixture of stimulations 

 and depressions caused by the action of morphine on the me- 

 dulla. Or if the pigment cells are controlled by the reflex irri- 

 tability of the spinal cord which may be depressed for a period 

 and then may be followed by an increased irritability. On the 

 latter hypothesis all the pigment cells should contract during 

 the heightened irritability or expand during the diminished 

 irritability; but since this is not the case it is probable that all 

 the regions of the spinal cord are not involved at the same time. 



If.. Caffeine. In embrj^os exposed to a 0.2 per cent to 0.25 per 

 cent solution of caffeine citrate no change occurred in the pig- 

 ment cells. The animals died in a much distorted condition. 

 The pigment cells disintegrated in two hours. A 0.05 per cent 

 solution of caffeine citrate caused the pigment cells to con- 

 tract in 4.25 minutes. There was a peculiar twitching of the 

 muscles which lasted twelve minutes. A depression occurred in 

 fourteen minutes. The pigment cells expanded very rapidly. 

 In 0.025 per cent caffeine citrate solution contraction of the pig- 

 ment cells took place in 5.25 minutes. The depression or paraly- 

 sis was elicited in thirty minutes in some, while in others it took 

 ■forty-five to sixty minutes. A solution of 0.005 per cent caffeine 

 citrate caused no contraction of the pigment cells in two and 

 one-half hours. 



The convulsions observed were quite similar to those that 

 occurred in strychnine. In caffeine the responses to shadows 

 were absent. If the dish was jarred the reactions were weaker 

 and lasted a short interval. These reactions occurred in solu- 

 tions ten times as strong as in strychnine. The response was not 

 opisthotonus, but the head was drawn toward one side and the 

 tail toward the other. There was no difference in the sides to 

 which the curvature occurred (as shown in text fig. 3). The 



