CHEMICAL AGENTS ON CHROMATOPHORES 181 



stimulation is followed by an expansion of the pigment cells. 

 The action of cocaine on the nervous system is in a series, 

 namely, the cerebrum is first affected, then the cerebellum and 

 medulla, and lastly the spinal cord. It also acts on the sen- 

 sory fibers and their terminations. 



Von Frisch ('11) observed that the local application of cocaine 

 caused the contraction of the melanophore in the minnow and 

 Carssius (sp.) . An injection of a 5 per cent solution into the body 

 cavit}^ caused a contraction of the pigment cells after the sym- 

 pathetic nerves were severed. He concluded that the action 

 of cocaine was through the central nervous system. Carlson 

 ('06) showed that weak solutions of cocaine had a primary stim- 

 ulating action on the heart ganglion of Limulus, but had no 

 effect on the heart muscle. Hedborn ('99) observed a slight 

 primary stimulating action on the isolated heart of the cat. 



It is probable that cocaine acts on the reflex center which 

 controls the pigment cells. It may act on the nerve endings of 

 the pigment cells. It is obvious that it will require a great deal 

 more of work to determine the relation of cocaine to the pigment 

 cells before any generalization can be made. 



9. Veratriyie. Solutions of veratrine of 0.5 per cent concen- 

 tration caused a rapid contraction of the pigment cells. The 

 contraction was complete in two minutes. Paralysis set in at 

 six minutes, and pigment cells were completely expanded in 

 two more minutes. In a 0.25 per cent solution the stages were 

 the same. In a 0.005 per cent veratrine solution the pigment 

 cells were completely contracted in nine minutes. The first 

 signs of paralysis appeared in eighteen minutes. Veratrine 

 was a very active agent in causing the contraction of the pig- 

 ment cells. Dilutions of 0.0005 per cent to 0.00005 per cent 

 caused a contraction of the pigment cells in eighteen to twenty 

 minutes. The paralytic expansion occurred in thirty minutes. 

 A solution of 0.00001 per cent veratrine caused no change in 

 the pigment cells. 



Veratrine acts on the medullary center and the spinal cord, 

 where a marked increase of irritability is elicited. After large 

 doses there is a paralysis of the centers. It acts on the periph- 



