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SCIENCE 



[N. S. Vol. LIII. No. 1375 



convincing demonstration of the otolitli func- 

 tion is that which can be obtained in the 

 absence of all other parts which could give 

 the same reaction. This I have been able to 

 accomplish in the most definite way (19206). 



My experiments on the otolith have been 

 made on several species of sharks and rays. 

 The most favorable animal for this purpose 

 is the shovel-nosed ray or guitarfish, Bhino- 

 iatus producius. I removed all three semi- 

 circular canals with their ampullae and then 

 washed out the large, soft, friable otolith of 

 the sacculus. There now remained only the 

 small otolith of the recessus. This otolith is 

 shaped somewhat like a plano-convex or con- 

 cavo-convex lens and rests in. a concave de- 

 pression in which it fits much like one saucer 

 standing in another. The concavity is lined 

 with the characteristic macular epithelium 

 with its hair cells. I found that if I pressed 

 on the anterior side of this otolith the eyes 

 rolled forward on their axes, anterior pole 

 downward, that is, they made the same move- 

 ment which occurs when the head is tilted 

 upward. If I pressed on the hinder margin 

 of the otolith the eyes rolled hackward on 

 their axes, the movement which occurs when 

 the head is tilted downward. Pressure ap- 

 plied to the right margin of the otolith caused 

 the right eye to he depressed and the left eye 

 to be elevated, the same movement which re- 

 sidts from rotating the animal to the left 

 around its longitudinal axis, and this resulted 

 whether the stimulus was applied to the 

 otolith of the right or left ear. The method 

 of stimulation just described very soon in- 

 jured the delicate otolith and the movements 

 could only be obtained a few times. Wten, 

 however, I placed a small pellet of wet 

 absorbent cotton on the otolith I could with 

 fine forceps pull the pellet backward or for- 

 ward or from side to side repeatedly without 

 apparent injury to the otolith. When the 

 cotton was pulled to the right the right eye 

 went down, when pulled to the left the left 

 eye went down, when pulled forward the 

 eyes rolled forward on their axis, when pulled 

 backward both eyes rolled backward. 



The above experiment shows that the 



a priori assignment of different functions to 

 different otoliths with reference to the planes 

 in which they lie and the rotational move- 

 ments of the body to which they correspond 

 does not accord with the facts. AU the com- 

 pensatory movements and positions arising 

 from vestibular stimulation are obtained from 

 this otolith alone. Parker's and my previous 

 observation that the large otolith of the sac- 

 culus is not concerned in equilibrium is con- 

 firmed. It is of interest, too, to note that the 

 otolith of each ear gives rise to complemen- 

 tary movements in both directions; elevation 

 of the right and depression of the left eye, or 

 depression of the right eye and elevation of 

 the left eye can be obtained from the otolith 

 of either ear. 



m. THE MECHANISM OF THE PHYSIOLOGICAL 

 ACTION OF THE OTOLITH ORGANS 



It has been almost universally believed 

 since the publication of the earlier papers of 

 Mach and Breuer that in the otolith organs 

 the normal stimulus is the pressure due to 

 the weight of the otolith resting on the sensi- 

 tive macular epithelium; when the position 

 of the head is changed the pressure is shifted 

 to a different part of the macula and a differ- 

 ent set of impulses is sent to the muscle 

 groups concerned. This conception has been 

 greatly strengthened by the work of Delage, 

 Kreidl and others on the otocysts of inverte- 

 brates. But as I have shown in the preceding 

 section stimulation experiments show with the 

 utmost clearness and regularity results which 

 are exactly the reverse of those which should 

 follow if the pressure theory were true. In 

 describing these experiments I have been re- 

 peatedly stopi)ed to answer the question, 

 " Don't you mean ' to the right ' when you 

 say ' to the left ' ? " or, " Don't you mean 

 ' backwards ' instead of ' forwards ' ? " When 

 the normal animal is rotated around its longi- 

 tudinal axis, to say 30° to the right, the 

 right eye goes up and the left eye goes down. 

 When the body is in this position the weight 

 of the otolith in each ear must be shifted to 

 the right. But when the right side of the 

 otolith is pressed upon or when the cotton is 



