718 
the board p-q-r-s is first revolved 90° about U-T, so that the animal 
is in lateral position, and when in this position the board is turned 
Fig. 1. 
about the axis V-W, the animal will revolve about its dorso-ventral 
axis. A combination of rotations round the axes U-T and V-W 
enables us to bring the animal in any given position in space. In _ 
all of them the direction of the nystagmus consequent on a cold- 
water flow could be determined. In the following expositions the 
rotations in the different directions are described : 
Rotation I. 
Animal in ventral position, mouth-fissure horizontal. Rotation of 
the animal on its bi-temporal axis. Direction of rotation: head down, 
tail up. 
Rotation U. 
Animal in ventral position, mouthfissure horizontal. Rotation of 
the animal on its occipito-caudal axis. Direction of rotation: douched 
ear downwards. | 
Rotation UI. 
Animal in lateral position with irrigated ear downwards, mouth- 
fissure vertical. Direction of rotation: head down, tail up. 
In these experiments the direction of the nystagmus consequent 
on a cold-water irrigation, was determined 37 times for every 
rotation of 360°. The first determination was always made at the 
normal position of that rotation; so e.g. at rotation I: the animal 
in ventral position, mouth-fissure horizontal. After this, while the ear 
was constantly being douched, the animal was moved every time 
10° in the given direction and the direction of the nystagmus was 
noted. At the 37% determination the animal had come round again 
