318 THE AMERICAN NATURALIST,- [Vou. XXXII, 
almost exclusively of nerve fibres, which for the most part run 
longitudinally along the spinal cord. Thus, if we cut the spinal 
cord transversely, we have a countless number of cross-sections 
of nerve fibres. But, although even under the microscope the 
whole field of white matter appears quite homogeneous, we 
know that it is divided into a number of fibre bundles of vary- 
ing significance and function. Thus we distinguish in each 
half section of the spinal cord about sixteen different regions. 
The nerves mentioned above, and which are of significance 
to us, enter the spinal cord through the posterior roots, and take 
their further course to the brain, perhaps exclusively by way of 
the posterior bundles (gs) and (64), the lateral cerebellar tracts 
(ks) and Gower’s bundle (g). 
I would not have bothered you with these dry anatomical 
data if we were not to need them later. 
I turn now to another class of sensations, which likewise are 
scarcely known to the non-scientific, since they, like the mus- 
cular sense, perform their function outside the sphere of con- 
sciousness, and become apparent only when they are irritated. 
Under this head let us consider the inner ear, that part of 
the auditory organ which lies deeply buried in the hardest bone 
of the skull, the temporal bone. We find in this two principal 
parts; one has the characteristic form of a snail shell, and is 
hence called the cochlea; the other consists of three curved 
tubes which are connected in such a way that the two ends 
of each open into a small sac-like enlargement, the utriculus. 
These tubes are called the semicircular canals; together with 
the utriculus they form the labyrinth of the ear. If one im- 
agines a plane passed through each of these three arches, it 
will be found that the three planes are perpendicular to one 
another. It is only when the cochlea itself becomes diseased 
or destroyed that a defect of hearing occurs. This effect is 
not produced by injuries to the labyrinth. In the latter case, 
on the other hand, very peculiar disturbances of the equilib- 
rium are experienced. These facts were first demonstrated by 
Flourens. I cannot here go further into the very interesting 
investigations which were carried out later, especially by Golz, 
Breuer, and Ulach, among others, for the determination of the 
