forehead and temple with tincture of iodine, etc. Electricity also does good service in the later periods of the disease, and although the electric treatment, on account of the deep position of the muscle, cannot act in so direct a manner as in the case of other muscles, still, some part of the electric current seems to be able to reach it.
The indications suggested by the presence of syphilitic, cerebral, or spinal disease, belong in the province of special pathology, and need not here be discussed.
To relieve the annoyance of diplopia, a pair of spectacles may be worn which cover the affected eye with a ground glass. The idea suggests itself of uniting the double images by means of prisms, but it is seldom practicable. The principal reason for this is that, even in a case of slight paralysis, the distance between the double images is too great to admit of their being united by prisms which could be worn as spectacles. Prisms of more than 6° or 7° can scarcely be worn for this purpose, partly because of their weight, partly because of their chromatic aberration. Even if both eyes were provided symmetrically with such prisms, the effect would be that of a prism of 12° or 14°, which would generally be insufficient.
Another essential reason against their use is, that the distance between the double images varies greatly with every change in the direction of vision. If, for instance, with paresis of the abducens on the right side there be single vision in the left half of the visual field, while during vision directed in the median plane diplopia is present, which could be corrected by a prism of 12° or 14°, it would still not be well to allow such prismatic spectacles to be worn. On account of the increased distance between the images in the right half of the field, they would not be sufficient to unite the double images during vision in this direction; while in the left half of the field, where there was normal single vision, the prisms would provoke crossed double images, and a compensating convergence of the visual axes. Under these circumstances a secondary contraction of the antagonistic muscle is induced, and the development of strabismus convergens is favored.
The correction of the diplopia by prisms is, then, indicated only when there exists secondary contraction of the antagonistic muscle, and, as a consequence of that, diplopia throughout the
