Especially important is the examination of the field of vision, as the seat of one of the most serious anomalies discovered by the Modern School, the presence of peripheral scotoma, frequently found in epileptics and born criminals. To test this anomaly, use should be made of Landolt's apparatus (Fig. 36). This consists of a semicircular band, which can revolve around a column. The patient rests his chin on a support placed in front of the semicircle in such a manner that the eye under examination is exactly in the centre, and looks directly at the middle point of the semicircle, corresponding to 0 in the scale: the testing object, a small ball, is passed backwards or forwards along the semicircle. A graduated scale, placed on the semicircle, marks the point limiting the field of vision, and the result is registered on a diagram. The average limit of the normal field of vision is 90 mm. on the temporal side, 55 mm. on the nasal side, 55 mm. above and 60 mm. below (see Fig. 42). If a suitable instrument is not available, a series of concentric circles may be traced on a slate and the patient placed at a certain distance with one eye covered. The examiner then touches the different points of the circles with his hand and asks the patient whether he can see it when his eye is fixed on the central point. In this way the various points limiting the field of vision are noted and furnish, when united, the boundary line. =FIG. 37 Diagram Showing Normal Vision= _Hearing_ is generally less acute in the criminal than in the normal individual, but does not show special anomalies. It may be tested by speaking in a low voice at a certain distance from the patient, or by holding an ordinary watch a little way from his ear. _Smell._ Olfactory acuteness is tested by solutions of essences of varying strength, which the patient should be requested to place in order, indicating the one in which he first detects an odour. Ottolenghi has invented a graduated osmometer which is easy to use. The criminal generally shows olfactory obtuseness. _Taste_ is tested in the same way as smell, by varying solutions of saccharine or strychnine dropped on to the patient's tongue by means of a special medicine dropper. The mouth should be rinsed out each time. Normal persons taste the bitterness of sulphate of strychnine in a solution 1:600,000; the sweetness of saccharine in a solution 1:100,000. The sense of taste is less acute in criminaloids than in normal persons, and is specially obtuse in born criminals, 33% of whom show complete obtuseness.