Since the disease, however, appears only in a very small percentage of all children who are surrounded by the unfavorable conditions men tioned, we must obviously assume an individual predisposition, in regard to the exact nature of which we can at present do no more than speculate. In some eases it is found that the children have been grad ually reduced by some chronic nutritional disturbance or febrile dis ease. Most of these are more or less rachitic; but it is not possible to demonstrate any neuropathic taint, nor does the condition appear to lead to any- other nervous disease. Rauclnitz offers thc ingenious suggestion that certain dynamic conditions in the eye muscles are the chief cause. If the muscles are naturally abnormal, even swill a slight injury as the lack of light might be enough to produce the nodding spasm and nystagnms.
The treatment of nodding spasm consists in securing better illumination and in improving the general condition of tbe children, if it is unfavorable, by suitable feeding. If this can be done, the prognosis is always absolutely favorable.
The only condition that might present diagnostic difficulties is juvenile or congenital nystagnitis if, as occasionally happens, it is asso ciated with isolated movements and oblique position of the head. The differential diagnosis can usually be made at. once, since in juvenile
nystagnius there is usually some definite cause (central macula, cataract, amblyopia, and the like). At any rate, the subsequent course of the disease will serve to clear up any doubt.
Similar tremors or nodding movements of the head, which may occur at the beginning of some organic nervous disease such as tuber culous meningitis (Demme), are at no time accompanied by nystag mils and, if due attention hs paid to the concomitant symptoms, should not be difficult to diagnose. The same is true of multiple, insular sclero sis and Freidreich's ataxia, in which, besides, the patients are always older.
Certain swaying or rolling movements observed in psy-chically abnormal and imbecile children sometimes exhibit great similarity to nodding spasm; but nystagmus is absent, anJI the movements them selves are less constant and not so much confined to the head. More over, the feeble-mindedness reveals itself early hy the objective signs. These movements will be described at greater length in the section on Sterotypias.
Finally, it should be briefly mentioned that the conditions de scribed as nodding epilepsy, or beckoning, saluting or salaam spasms must be sharply distinguishe(I from nodding spasm, to which they also pre sent some superficial resemblance. These anomalies belong to epilepsy.