With the field thus narrowed for us, it is surely legitimate, in the necessary scarcity of anatomical records referring directly to the state of the nerve-roots in ordinary neuralgia, to place great weight on the facts of a disease like locomotor ataxy, in which the main anatomical change is a progressive atrophy of the posterior columns which usually falls with peculiar severity on the posterior nerve-roots, or on the parts of the gray matter immediately adjoining these, and in which neuralgia may be said, for practical purposes, to be a constant and most characteristic phenomenon. If any one desires to see how strikingly the connection of the neuralgic phenomena with the anatomical-change comes out, I recommend him to study Dr. Lockhart Clarke's papers on locomotor ataxy (_vide_ "St. George's Hospital Reports, i." 1866; _Lancet_, June, 10 1865; "Med.-Chir. Soc. Transactions," 1869), or the excellently reported case by Nothnagel (_Berlin Klin. Wochensch._, 1865). It is really not too much to say that the only important difference between the clinical aspect of the pains of locomotor ataxy and those of ordinary neuralgia is simply such as depends on the fact that the anatomical change in the former case is bilateral, and usually affects the roots of several, sometimes of a great many pairs of nerves. I infer, from a conversation with Dr. Clarke, that he fully recognizes the force of the analogy, and the great strength of the presumption which it sets up in favor of an atrophic change of the posterior roots in neuralgia. It may, of course, be urged, against the view that neuralgia depends on any change analogous to those which occur in ataxy, that quantities of cases of the former recover speedily, and must be supposed to be either independent of material change altogether or, at any rate, to have involved only very trivial anatomical changes, not formidable diseases, like atrophy of nerve-centres. I find it impossible to admit that this argument has the slightest force. Are we to suppose that the posterior nerve-roots alone, of all tissues and organs of the body, are incapable of minute and partial changes in the direction of molecular death which may be perfectly recovered from in weeks, months, or even days? I, for one, cannot doubt, that such changes are of frequent occurrence, in all parts of the central nervous system, when I can consider the absolute dependence of these portions of the organism upon a perfect blood-supply, and the immense number of possible causes of temporary interference with that source of nutrition. And I can see no probable difference, except in degree and persistence between the effects on sensation which would be produced by such a change of the posterior roots as this, and that which would result from the more serious and fatally continuous change which is involved in locomotor ataxy.