The usual result of this is, first a relaxing of binocular vision, and as together with this the motive for convergence, namely, the effort of the accommodation ceases, the conditions for the commencement of divergence are produced. Still the elastic tension of the ocular muscles decides even here; if the interni preponderate, convergent squint results, when the myopic eye is used for near objects, the emmetropic for distant ones. If the externi preponderate, then permanent or periodic divergent strabismus is caused. Nevertheless, in a remarkable minority of cases the elastic tension of the ocular muscles is so regulated that, despite relaxation of binocular fusion, neither convergent squint nor absolute divergence occurs, but simple relative divergence remains with employment of the myopic eye for near objects. DYNAMIC SQUINT, INSUFFICIENCY OF THE INTERNI AND MUSCULAR ASTHENOPIA. The habit of binocular single vision, when it has once reached its normal development, governs the movements of our eyes to a great degree; the desire to avoid double images makes itself continually felt; and where this is not possible, an uncomfortable feeling of uncertainty arises at every movement of the body. Double images are prevented as far as possible by movements of the eyes, which we must designate as voluntary when we are conscious of their occurrence. If we follow a moving object with the eyes, the latter make corresponding movements in order to keep the image in the centre of both retinæ. For example, if we look at a distant object which approaches in the direction of one visual axis, this eye will necessarily remain still, while the other will be put into convergence in proportion as the object advances. If this did not happen, if this eye remained also immovable, the retinal image would deviate outwards more and more from the macula lutea and diplopia would arise. In order then to avoid diplopia the macula lutea moves to where the retinal image is formed. We can, however, move the images on the retina by the aid of prisms without movement of the object. If, for example, we hold a prism before the eye so that the base lies towards the temporal side, the retinal image will be displaced towards the base of the prism, outwards then from the macula, and double images will occur, which are at once removed by a distinctly perceptible inward movement of the eye. In this way, by means of a prism applied with the base inwards, outward deviation may be produced, and even in a modified way deviations in height of the visual axes by means of prisms with the base upwards or downwards. Here the force of habit is apparent, for in the daily use of our eyes we continually practise the inward movement of the visual axes; we can also easily restore the customary degree of convergence by means of prisms with the bases outwards; physiologically indeed, it is quite immaterial whether an object is in a proximity to our eyes attainable by