CASE 54.--Ida K--, æt. 11. On the right, hypermetropia 3 D. with the ophthalmoscope, visual acuteness 5/24. No. 0·3 is read with difficulty. On the left, with the ophthalmoscope hypermetropia 4·5 D. with asymmetric meridian. Single letters of 3·0 m. are recognised with convex 6·5 D. Fingers are counted at about 1-1/2 m. The choroid is slightly and unequally pigmented, no ophthalmoscopically assignable reason exists for the considerable visual defect. The left eye frequently deviates outwards, convergence is attainable to 15 cm. On May 2nd, 1877, shortening of the internus (without tenotomy of the externus). Two weeks later slight convergent squint was present; in November, 1877, six months after the operation, the position of the left eye was perfectly normal. Tenotomy of the externi suffices when the divergent deviation is inconsiderable and does not occur often, if the normal near point of convergence can still be reached, and binocular fusion is possible. If we want to increase the effect of simple tenotomy of the externi, this may be done just as well by practice of the associated movements of the eyes as by practice of the convergence, of course for a short time only after the operation. As long as the detached tendon of the external rectus is not re-attached firmly with the sclerotic, all these movements of the eyes help to strengthen the result of the tenotomy. In order to practise convergence we can bring a suitable fixed point on to a mirror and so make it possible for the patient himself to see the position of his eyes, of course only in cases where binocular fusion is no longer present. He who possesses a normal binocular vision is troubled in these exercises by diplopia; but this is not the case in the suppression of binocular fusion so frequent as a result of squint. Periodic divergent squint is divided by no sharply defined limits from those cases in which only a preponderance of the externi exists without insufficiency of the interni. We frequently find very considerable degrees of facultative divergence as a casual symptom, without the occurrence of manifest divergence or the presence of asthenopic troubles. If this is accompanied by weakness of the interni, absolute divergence occurs on looking at near objects, sometimes for distance also and certainly if we suppress binocular fusion by covering one eye or render it difficult by colouring one visual field with a red glass. In these cases the indications for the operation are given either by asthenopia, by troublesome double images or by the disfigurement inseparable from periodic squint; it will depend on the degree of the facultative divergence, whether we confine the tenotomy of the externus to one eye or whether we distribute it between both eyes.