THE SENSE OF MOVEMENT - DYNAMIC SENSE 791 



in these sensations and behave normally unless subjected to unusual 

 conditions. Thus, the tests of James 1 have proved 186 among -500 

 deaf persons to be without vertigo when rotated, and 15 among 25 

 deaf persons to lose their sense of orientation while diving. Normal 

 persons, of course, behave very differently; 199 of the 200 examined 

 displayed vertigo and forced movements. 



The general weakness of the musculature following injuries to 

 the labyrinth, is attributed by Ewald to a loss of the labyrinthine 

 tonus, mediated by a set of impulses which reflexly keep the mus- 

 culature in a state of alertness. This effect is obtained through the 

 intervention of the cerebellum with which the labyrinth is in close 

 functional relation. Thus, we find that the vestibular fibers of the 

 auditory nerve terminate in the nucleus of Deiters and the nucleus 

 of Bechterew, where reflex connections are formed with the cranial 

 nerves and the different motor centers. Connections are also estab- 

 lished here with the nucleus fastigius and the cortex of cerebellum. 

 The semicircular canals, therefore, serve as a sense-organ of the 

 cerebellum, this central structure enabling the sensations derived 

 from them, to influence the tonus and behavior of the musculature 

 and hence, also muscular coordination and the equilibrium. 



The Activation of the Hair-cells of the Ampulla. The first definite 

 explanation of the action of this receptor has been given by Goltz 2 

 who assumed that the endolymph of these canals rests upon the 

 sensory epithelium with a certain pressure and that this pressure 

 changes with the position of the head. But, while he regards them 

 very distinctly as organs of equilibration, he seems to believe that 

 they are activated solely by hydrostatic differences. This principle 

 has been more fully developed by Brener, 3 but this investigator 

 abandons the hydrostatic factor or gravitation almost altogether 

 and puts in its place a hydrodynamic mechanism. This amplified 

 theory which has been materially strengthened by a number of observa- 

 tions made by Mach and Brown, 4 brings forth the conception that the 

 hair-cells constitute the peripheral elements of equilibrium, and that 

 their activation is accomplished by the changes in the pressure which 

 the endolymph must suffer whenever the canals are moved. Thus, it is 

 assumed that the different movements of the head give rise to oscil- 

 lations of the endolymph which in turn affect the position of the hair- 

 like processes of the ampullar lining cells. To be sure, the simple 

 effects of gravity cannot be excluded altogether, but this theory 

 subordinates the latter completely to those of movement. 



If a tumbler is filled with water and is twirled upon a rotating disc, 

 it will be noted that its walls move first, while the water lags behind, 

 and exerts a pressure in the opposite direction. If the twirling is 



. Jour, of Otology, 1887; also: Kreidl, Pfluger's Archiv, li, 1892, 119. 



2 Pfluger's Archiv, xxx, 1870, 172. 



3 Sitzungsb. der Akad. zu Wien, cxii, 1903. 



4 Jour, of Anat. and Physiol., viii, 1874, 327. 



