578 



There are, liowever, also otliei- slimiili wliicli acl n|)oii tlie "in- 

 hibitory reflex", stimuli acting npoii other senses liiaii the hydrostatic 

 organ of sense (the air-bladder filled witii gas) are also amongst them. 



The following were made to act u|):)n fishes: light stimnli, vibra- 

 tions of the water (whether they are to be viewed as sonnd or 

 sensory stimuli I shall leave undiscussed for the present), stimulation 

 of the static organ, chemical stimuli, enclosure in a narrow space 

 (this must not be viewed as the stimnlaliou of a certain organ of 

 sense, Imt as a means of exciting terror). 



a. Light-stiiuuli. 



The fishes in the experimental basin nearly always went to the 

 darkest part. If the basin is lighted up, they turn away from the 

 light, but do not become restless. This is the case, however, if the 

 basin is alternately lighted and darkened. If, for instance, the basin 

 is alternately lighted and darkened about 120 times a minute, the 

 fish begins to swim round uneasily, the respiration-rhythm rises 

 from about 50 to about 90 a minute, the mouth is opened every 

 now and then, and finally some air-bubbles escape. 



h. Vibrations in the water. These are brought about by tapping 

 (with a stick) against the experiment-bottle which was in the basin, 

 and which contained the fish. The results agree with those mentioned 

 under a. 



c. Stimulation of the static* organ. 



If a fish is placed in a bottle completely filled with water, which 

 is closed by means of a tight fitting stopper, and if the bottle is 

 swiftly turned round in all directions, then the tish is compelled to 

 correct continually its static position. Within a very short time such 

 an animal emits a number of air-bubbles. 



d. Chemical stimuli. 



When fishes are narcotized in the water with ether or chloroform, 

 they often emit air-bubbles. 



e. Fishes enclosed in a narrow space, which are, for instance, 

 put in a jar below the surface of the water in the basin, emit a 

 few air-bubbles, swimming up and down meanwhile in a state of 

 great agitation. 



We conclude from the preceding that as a result of greatly dif- 

 ferent sensory stimuli, besides swimming and respiratory movements, 

 the opening of the sphincter also manifests itself as a retlex. 



Finally I wish to point out that these experiments with various 

 stimuli were also carried out with fishes that had been operated 

 upon. Thus I hoped to obtain a clue as to the direction in which 



