MOVEMENTS IN THE VISUAL CELLS 173 



maining 10 minutes in the dark the jar was removed into strong dif- 

 fuse dayhght for Ij hours. During this time, the fish was practically 

 motionless except for a very weak but rhythmical pulsation of the oper- 

 cular rims. At the end of the experiment one eye was removed and 

 fixed. The Ameiurus was allowed to recover until the next day when 

 the other eye was removed. The pigment in the eye which had been 

 subjected to carbon dioxide was in the typical dark position (cf. fig. 4) 

 while the pigment of the control eye was maximally expanded (cf. 

 fig. 2). Titration of the anaesthetizing solution showed that the 

 concentration of carbon dioxide had been in the ratio of 60.14 cc. per 

 litre of water. 



In the converse experiment from light to darkness an Ameiurus 

 lived 3 hours in a similar .solution (53.07 cc. of carbon dioxide 

 per litre) during which time the pigment retained its light dis- 

 tribution, whereas the control eye removed on the next day, 

 showed maximal contraction. 



These results prove conclusively that in the presence of certain 

 concentrations of carbon dioxide the pigment cells are not injured 

 but are in a condition of anaesthetization whereb}' there is a 

 failure to respond to the normal stimulus causing contraction 

 and expansion. Such experimentation, however, does not show 

 whether this failure is due to a direct effect upon the pigment 

 cells or to an inhibition through the central nervous system. 



To demonstrate which alternative is true, the effect of carbon 

 dioxide was tested on excised eyes of Ameiurus. If, under these 

 conditions, a migration occurs a direct influence of the anaesthetic 

 on the cell itself will be disproven, while on the other hand, 

 if no migration ensues one can only infer that a similar direct 

 action on the pigment cell is responsible for the whole course of 

 events in the living fish, whereas an inhibition through the cen- 

 tral nervous system may be involved as well. 



For such an experiment the excised eye of Ameiurus is well 

 adapted, since its pigment has been shown to migrate from the 

 dark to the light position, although the reverse process does 

 not occur. Excised eyes of dark-adapted fish were exposed to 

 light in a solution of carbon dioxide having a strength of about 

 60 cc. per litre. The pigment in each case was arrested in the 

 contracted position. 



