PHYSIOLOGY OF CHROMATOPHORES OF FISHES 561 



neglected by this author. The problem, upon last analysis, con- 

 sisted of the separation of a specific heat effect from that obtained 

 by heating the fluid surrounding the chromatophores, and thus 

 driving off a certain amount of the absorbed oxygen. 



Two types of experiments were carried out with the scales of 

 F. heteroclitus each one being repeated a number of times with 

 uniform results. 



April 11, 1912 



Scales from a 7 cm. female were placed in a 0.1 M NaCl solution until 

 fully expanded. A number of these were now removed to a 3-inch speci- 

 men bottle (fig. B) filled with 0.1 M solution of NaCl. This bottle 

 was then closed with a one-hole rubber .stopper, care being taken to 

 eliminate every trace of air. A thermometer was now easily inserted 

 into the salt solution through the hole in the stopper and when the ap- 

 paratus was completed the bottle was without an air-bubble. This 

 bottle was now immersed in warm water until the temperature of the 

 salt-solution had risen to 32°C. At this temperature all the melano- 

 phores were completely contracted. The bottle was then removed to 

 cold water until the thermometer within registered 19°C. Even before 

 this temperature was reached the melanphores had begun to expand 

 and at 19°C. this expansion was practically complete. This procedure 

 was repeated ten times on the same set of scales and ten distinct con- 

 tractions and ten expansions were observed in this way. Such changes 

 in the melanophores were perfectly obvious to the naked eye. At the 

 end of the experiment the bottle was still entirely free from air-bubbles. 

 Sixteen hours after the last expansion the pigment of the melanophoies 

 were still active. 



In this experiment it is clear that (1) all central nervous system 

 and hence psychic influences were absent; (2) there was no pos- 

 sibility of a loss of oxygen in the salt solution since the bottle 

 was absolutely air tight. Hence it follows that this contraction 

 of the melanophores at 32°C. must have been the result of a 

 specific heat stimulus. 



A second type of experiment was as follows. 



April 9, 1912 



A specimen bottle containing about 10 cc. of a 0.1 M NaCl solution 

 was immersed in a water bath in which the temperature was kept con- 

 stant (at 26°C.) by circulation from a tank regulated by a gas thermostat. 

 After the temperature of this NaCl solution had become constant, 

 scales from a 7.5 cm. female were placed in the specimen bottle. This 



