CHEMICAL AGENTS ON CHROMATOPHORES 179 



no change was elicited. In all the cases where paralytic expan- 

 sion occurred, it appeared fii*st on the ventral side. The reason 

 for this is not understood. 



Redi (1634) according to van Rynberk ('05) observed that 

 eels which died in a tobacco solution became lighter in color. 

 Cushny ('10) says, that in nicotine the spinal cord is thrown 

 into a condition of exaggerated irritability and that the medulla 

 seems to be involved to a greater degree than the spinal cord. 

 The stimulation does not involve the higher brain centers. Carl- 

 son ('06) observed that nicotine in weak solutions stimulated the 

 heart ganglion of the Limulus heart. This primary stimulation 

 was followed by a depression. There was no primary stimula- 

 tion of the heart muscle. Gee ('13) has found that in a solution 

 of 0.00066 per cent of nicotine leeches were vigorously stimu- 

 lated, which was followed by a depression of movements. Ro- 

 manes ('77) found that violent spasms were incited in the 

 medusae Sareia (sp.) and Tiaropsis when exposed to nicotine. 

 He also observed various distortions. Langley and Dickson 

 ('90) concluded that nicotine acts directly on the nerve cells and 

 not on the muscle. 



It is known that nicotine first stimulates and later paralyzes 

 the ganglionic cells of the sympathetic system, whether applied 

 directly to them or injected into the circulation. It is quite 

 probable that nicotine affects the sympathetic system of the 

 pigment cells, for there is first a contraction of the cells which is 

 later followed by an expansion. 



7. Atropine. Strong solutions (0.5 per cent) produced no change 

 in the pigment cells. The fish lived four hours in this concen- 

 tration. In 0.025 per cent solution of atropine sulphate, there 

 was no change in the pigment cells. All possible concentrations 

 were tried, but none of them produced a contraction of the 

 pigment cells. 



Pigment cells were contracted in 0.005 per cent strychnine 

 solution and then were transferred to solutions of 0.05 per cent 

 to 0.0025 per cent of atropine, where all the pigment cells ex- 

 panded rapidly. The expansion was complete from two to 

 four minutes. Pigment cells contracted in potassium salts were 

 expanded just as those that were contracted by strychnine. 



