Fig. 34
Esthesiometer
General Sensibility and Sensibility to Touch and Pain. Tactile sensibility should be measured by Weber's esthesiometer, which consists of two pointed legs, one of which is fixed at the end of a scale graduated in millimetres, along which the other slides (see [Fig. 34]). After separating the two points three or four millimetres, they are placed on the finger-tips of the patient, who closes his eyes and is asked to state whether he feels two points or one. Normal individuals feel the points as two when they are only 2 mm. or 2.5 mm. apart; when, however, tactile sensibility is obtuse (as in most criminals) the points must be separated from 3 to 4.5 mm. or even more, before they are felt as two. Obtuseness varies with the type of crime committed habitually by the subject; in burglars, swindlers, and assaulters, being approximately double, while in violators, murderers, and incendiaries it stands in the ratio of 5 to 1 compared with normal persons.
In the absence of an esthesiometer, a rough calculation may be made by using an ordinary drawing compass or even a hairpin, separating the two points and measuring with the eye the distance at which they are felt to be separate.
General Sensibility and Sensibility to Pain are measured by a common electric apparatus (Du Bois-Reymond), adapted by Lombroso for use as an algometer. (See [Fig. 35].) It consists of an induction coil, put into action by a bichromate battery. The poles of the secondary coil are placed in contact with the back of the patient's hand and brought slowly up behind the index finger, when the strength of the induced current is increased until the patient feels a prickling sensation in the skin (general sensibility) and subsequently a sharp pain (sensibility to pain). The general sensibility of normal individuals is 40 and the sensibility to pain, 10-25: the sensibility of the criminal is much less acute and sometimes non-existent.
Sensibility to Pressure. Various metal cubes of equal size but different weight, are placed two by two, one on each side, on different parts of the back of the hand. The patient is then asked to state which of any two weights is the lighter or heavier. This sense is fairly acute in criminals.
Sensibility to Heat. Experiments are made by placing on the skin of the patient various receptacles filled with water at different temperatures. If great exactitude is desirable, Nothnagel's thermo-esthesiometer should be used. This is an instrument very similar to Weber's esthesiometer, but the points are replaced by receptacles filled with water of varying heat and furnished with thermometers. The patient must state which is the colder, and which the hotter spot. Sensibility to heat is less acute in criminals than in normal individuals.
Localisation of Sensibility. After the patient has been requested to close his eyes, various parts of his body are touched with the finger and he is asked to point out the exact spot touched. Should he not be able to reach it with his finger, a statuette should be placed before him on which he should mark with a pencil the part touched. Normal persons are always able to localise the sensation exactly: inability to do so signifies disease of the brain or some kind of anomaly.
Sensibility to Metals is tested by placing discs of different metals, copper, zinc, lead, and gold, or the poles of a magnet, on the frontal and occipital parts of the patient's head. Sometimes he feels pricking or heat, giddiness, somnolence, or a sense of bodily well-being. In general, criminals show great sensibility to metals; in hysterical persons this sensibility reaches an extraordinary degree of acuteness. By applying a magnet to the nape of the neck, the sensations of such individuals become polarised, that is, what appeared white to them before becomes black; bitter, what was formerly sweet, or vice versa. This is an excellent way of distinguishing between bona-fide cases of hysteria and sham ones. My father once detected simulation in a soi-disant hysterical patient by means of a piece of wood shaped and coloured to represent a magnet. On application of either magnet, the real or sham one, the patient's sensations were identical, whereas hysterical persons experience very diverse sensations and are able to distinguish very sharply between the contact, not only of wood and metal, but of the different kinds of metal, and are particularly sensitive to the magnet.
| Fig. 35 | Fig. 36 | |
| Algometer (see [page 246]) | Campimeter of Landolt (Modified) (see [page 249]) |