of EdinhuTfjh, Session 1883-84. 
439 
by the latter. It may altogether he laid aside that the primary 
position of the eyes is that of rest. Landolt says — “ It is impossible 
for any one who has not practised to that end to give his eyes a 
direction absolutely parallel, especially in strabismus.” How he 
arrived at this result I do not know, but probably with the inge- 
nious apparatus of Javal, which requires a candle near the patient’s 
face and a dark room. 
Convergence without any definite point of view, therefore, must 
probably be considerable. Even the centre for the contraction of the 
pupil by light, which is regarded as a typical example of a reflex 
instead of a tonic ganglion during waking hours, is not improbably a 
tonic one naturally, for the pupil is semi-contracted during sleep, 
and dilates the moment a person wakes up. Whenever a distant 
object is viewed, impulses must ascend from the retina to inhibit 
reflexly the ciliary muscle, for it has no antagonist. It is just as 
easy to extend the process to the centre for the contraction of the 
iris, and suppose that the activity of some other centre exerts, 
during waking hours, an inhibition over the tonic moiety of nervous 
energy for the sphincter pupiili. This indeed might throw light 
upon the Argyll Robertson symptom of locomotorataxia and spinal 
myosis in general. It is impossible at present to decide, but I am 
inclined to believe that the position of rest for each person is that 
point of space for which accommodation and convergence are equal. 
Opinions, however, will probably vary between this point and others 
at a greater distance, but none will entertain parallelism. 
These facts increase the difficulty of ascertaining the exact inter- 
axial distance between the two eyes ; indeed, the name would be 
better changed to intercentral distance, as I have taken the liberty 
of doing in this paper. A glance at fig. 8 will show that the condi- 
tions would not be altered in the least, if the holes were drawn 
out into two parallel tubes, since the object is at practically infinite 
distance. If a screw were adapted to these tubes for their mutual 
approximation, or the reverse, they would resemble the visuometer 
for determining the interaxial distance. 
It is conceivable that many subjects might aver that they saw 
the same object through both tubes, when in reality the objects 
were not completely fused. The error introduced is due to the fact 
