THE CAUSE OF SEA-SICKNESS. 363 



their ends with the bag or vestibule. These run in three different 

 planes, and are lined with hair-like nerve-filaments, which are much 

 more abundant and more sensitive at the anterior part of the tubes. 

 The tubes are filled with liquid in which float little calcareous par- 

 ticles, the otoliths. These tubes are known as the semicircular canals. 

 It was difficult to see what connection with the sense of hearing these 

 canals could possibly have, and some time ago it was noticed that in- 

 juries to these impaired the sense of hearing in no way, but caused most 

 curious effects in the loss of equilibrium. 



For instance, in pigeons, when the vertical canal was cut, the bird 

 turned a series of back somersaults ; and, when the horizontal canal 

 was cut, the pigeon whirled around in an horizontal plane, in every case 

 tending to rotate in the plane of the canal which was cut. And what 

 is especially interesting to us is, that in these and other experiments 

 iritation or injury to these canals was almost invariably followed by 

 vomiting. Experiments, by Professor Ferrier and others, point to a 

 very close relation between these canals and the sense of equilibrium, 

 and an especially strong suggestion is given by the disease known as 

 labyrinthine vertigo, or Meniere's disease. This is characterized by an 

 irritated and congested condition of these semicircular canals, due to 

 some internal cause, and its symptoms are the same throbbing in the 

 head, the pale, cold skin, and vomiting, as in sea-sickness, and in 

 addition the patient reels and staggers, being unable to keep his bal- 

 ance. In this disease we seem to have the exact reverse of sea-sick- 

 ness, the irritated condition of the canals causing the unusual move- 

 ments of the body ; whereas in sea-sickness we have the unusual move- 

 ments of the body which result from the pitching of the ship, causing 

 the irritation of the canals, and in both'cases the irritated state of the 

 semicircular canals is accompanied by vomiting. The mechanical ex- 

 planation of why such irregular motion should cause irritation of the 

 canals seems simple. By the pitching movements of the ship, which 

 are by far the worst, the head is carried backward and forward 

 through a long arc. At the end of the descent the head stops, but by 

 its inertia the fluid in the canals rushes on and washes the otoliths up 

 against the nerve-filaments at the front of the canals. These are ex- 

 tremely sensitive, and the repetition of this process a few times serves 

 to establish an excessive irritation which is expressed by giddiness and 

 vomiting. Why such gradual motions should cause sea-sickness, while 

 much more violent ones, such as horseback-riding, do not, can only be 

 explained by saying that in the more violent ones the individual has a 

 stimulus to adapt his positions to the motion, which he has not in the 

 often unnoticed pitching of a ship. At any rate, this theory explains 

 why lying down should afford relief, as the otoliths then rest at the 

 back and less sensitive part of the canals ; and it also explains why 

 riding backward should cause nausea and giddiness, as here, of course, 

 the otoliths drag behind and irritate the anterior parts of the canals. 



