No. 388.] MAINTENANCE OF THE EQUILIBRIUM. 327 
number of deaf-mutes, in about fifty-six per cent of whom the ear 
labyrinth is entirely degenerated. Such deaf-mutes go tottering 
and stumbling along with their legs spread far apart ; if, while in 
the water, they become submerged, they lose their orientation 
in space. But, as can be easily understood, and as has been 
demonstrated by Kreidl, they are free from whirling dizzi- 
ness ; likewise (according to the investigations of Pollak) they 
are immune from galvanic dizziness, which is produced in a 
normal individual when a galvanic current is passed through 
the head. 
We have seen that through the abnormal or arrested activity 
of a number of sensory nerves, disturbances of equilibrium and 
dizziness are produced; we must now go farther and investi- 
gate the action of the central nervous system in this relation. 
We here pass to so wide a field of observation, however, that 
I must limit myself to indicating only the rudest outlines. 
The cerebellum has been recognized as the most important 
central organ of equilibration. Severe diseases of the cerebel- 
lum are therefore characterized by dizziness and loss of equilib- 
rium. The gait of one thus diseased is peculiarly unsteady, 
best compared to that of a drunken man. In this case also 
irregular motions result, but still they are quite different from 
those I have described for tabes. This kind of defective mo- 
tion is called cerebellar ataxia. 
But a glance at our diagram shows that another part of the 
central nervous system plays a réle in keeping the balance. We 
are next to consider that nerve tract by means of which the 
cerebellum exerts its regulatory influence upon the tract control- 
ling motion. 
In the diagram (Fig. 2) I have indicated this tract by a 
dotted line, in order thus to express the fact that its course is 
not perfectly known to us. But notwithstanding this somewhat 
unsatisfactory condition of our knowledge, we must expect that 
similar phenomena can be produced from different places in the 
brain. i 
Dizziness with severe disturbances of the equilibrium may 
occur, the brain parts concerned being severely diseased. It 
is sufficient for them to experience a changed or imperfect 
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