RHEOTROPIC RESPONSES OF EPINEPHELUS STRIATUS 451 



study of the hamlet's cutaneous end organs. Of these only the tactile 

 corpuscles are significant, because the receptors for chemical, photic 

 and thermal stimuli plainly can not be involved in these rheotropic 

 responses. 



It has been stated previously that the areas of greatest cutaneous 

 sensitivity in the case of both touch and current stimulation have the 

 same distribution. Cocaine is known to inhibit the functioning of 

 the end organs of touch. It was, therefore, used to eliminate, func- 

 tionally, the tactile corpuscles, in order that their relation to rheo- 

 tropism might be determined. Of all available areas the lips were 

 chosen for the application of this reagent because the experiments had 

 shown that their stimulation gave the most marked and peculiar re- 

 sponses. Whether the lips are stimulated by a fine glass rod or by a 

 moderate water current, the fish performs the very curious reaction of 

 either backing away violently or of standing on its head. The method 

 of treatment with the cocaine was as follows: the fish was removed 

 from the experiment tank and the lips were immediately immersed in 

 a 0.1 per cent solution of sulphate of cocaine for about ten seconds; 

 this was supplemented by bathing the lips with the same solution ap- 

 plied by means of a soft cloth at about ten-second intervals for fifty 

 seconds. After this treatment the fish was returned to the tank and 

 its responses to stimulation by a glass rod and by a weak current 

 (about 1/28 liter per second) were noted. By a repetition of the treat- 

 ment it became evident that there was a slowing down in time of re- 

 sponse with increased exposure to the solution and that this was pre- 

 cisely the same for both types of stimulation. Two repetitions of the 

 first treatment in all about three minutes were usually sufficient to 

 inhibit completely all responses to either type of stimulation; neither 

 the glass rod nor the localized current then produced any reaction. In 

 subsequent trials the lips were treated continuously without periodic 

 subjection to stimulation for a period of about three minutes. The 

 effect was the same as in the preliminary treatment just described. 

 After such administration of cocaine the fish swam about in a slightly 

 abnormal manner, manifesting an irritation due, doubtless, to the 

 drug. This insensitivity of the lips lasted about a minute, sometimes 

 a few seconds longer. Then a gradual functional recovery occurred 

 until, at the end of three to four minutes, normal responses could be 

 obtained by the use of either stimulus. It is most significant that the 

 time of disappearance of normal sensitivity, as well as that of its re- 

 appearance, was absolutely the same for both kinds of stimulation. 



