In this country, however, there is as yet no disposition to give up the phrase locomotor ataxy, and it only remains to define with sufficient care the class of cases to which the word is here meant to apply. The disease is understood to depend upon a degeneration of the spinal cord, of which the following description is given by Lockhart Clarke:[50] "In true locomotor ataxy, the spinal cord is invariably altered in structure. Its membranes, however, are sometimes apparently unaffected, or affected only in a slight degree; but generally they are much congested, and I have seen them thickened posteriorly by exudations, and adherent, not only to each other, but to the posterior surface of the cord. The posterior columns, including the posterior nerve-roots, are the parts of the cord which are chiefly altered in structure. This alteration is peculiar, and consists of atrophy and degeneration of the nerve fibres to a greater or less extent, with hypertrophy of the connective tissue, which give to the columns a grayish and more transparent aspect; in this tissue are embedded a multitude of corpora amylacea. Many of the blood vessels that travel the columns are loaded or surrounded to a variable depth by oil-globules of various sizes. For the production of ataxy, it seems to be necessary that the changes extend along a certain length, from one to two inches of the cord. The posterior nerve-roots, both within and without the cord, are frequently affected by the same kind of degeneration, which sometimes extends to the surface even of the lateral columns, and occasionally along the edges of the anterior. Not unfrequently the extremity of the posterior cornua, and even deeper parts of the gray substance, are more or less damaged by areas of disintegration. The morbid process appears to travel from centre to periphery, that is, from the spinal cord to the posterior roots. In the cerebral nerves, on the contrary, the morbid change seems to travel in the opposite direction, that is, from the periphery toward the centres. From the optic nerves it has been found to extend as far as the corpora geniculata, but seldom as far as the corpora quadrigemina. With the exception of the fifth, seventh, and eighth pair, all the cerebral nerves have occasionally been found more or less altered in structure." The symptoms which occur in cases in which the above are the morbid appearances found after death are (roughly speaking) as follows:[51] "A peculiar gait, arising from want of co-ordinating power in the lower extremities, a gait precipitate and staggering, the legs starting hither and thither in a very disorderly manner, and the heels coming down with a stamp at each step." No true paralysis in the lower extremities or elsewhere. Characteristic neuralgic pains, erratic paroxysmal in the feet and legs chiefly--pains of a boring, throbbing, shooting character, like those caused by a sharp electric shock.