COMMON SENSATION. PAIN. 935 



course of a sensory nerve the latter may lose its function at the site of the 

 affection, so that peripheral impressions can no longer be perceived. 

 If the painful irritation affects the central extremity of the nerve- 

 tract, it will still be referred to the peripheral extremity of the nerve. 

 In this way there arises the apparently paradoxical condition of painful 

 anesthesia. It is noteworthy that pain-sensations cannot be localized 

 with precision. The localization succeeds best when the irritation 

 is applied peripherally to a small area (for example a pin -prick). When, 

 however, the stimulation is applied in the course of the nerve, or in 

 the center, or to nerves whose peripheral extremities are inaccessible 

 (such as the intestines), pain results that cannot be localized (for ex- 

 ample belly-ache). When the pains are severe the phenomenon of 

 irradiation of pain is added, in consequence of which localization is 

 impossible The pain rarely continues in uniform degree, but there 

 occur, as a rule, exacerbations and remissions in the intensity and also 

 paroxysmal exacerbations. This probably is due to the fact that pain 

 often results from a summation of irritations, each of which causes no 

 pain of itself. 



The intensity of the pain depends first upon the irritability of the 

 sensory nerves. In this respect there are important individual varia- 

 tions, some nerves, for example the trigeminus and the splanchnic, 

 being extremely sensitive as compared with others. The greater the 

 number of nerve-fibers affected the more severe is the pain. Finally, 

 the duration is of importance, as the same irritation, long continued, 

 may cause an intensification of the pain beyond the point of endurance. 



According to the character of the sensation the pain is described, 

 as stinging, cutting, boring, burning, shooting, throbbing, pressing, 

 gnawing, tearing, twitching, and dull, the causes for the differences 

 being, however, entirely unexplained. Painful sensations are abolished 

 by anesthetics and narcotics, such as ether, chloroform, morphin, etc. 



The best means for testing cutaneous sensibility consists in the employment 

 of constant or induced electrical currents. The minimum of sensibility is deter- 

 mined as that strength of current that excites the first trace of sensation ; and also 

 the minimum of pain, that is, the weakest current that first excites distinct pain. 

 The electrodes are metallic, about the size of a knitting-needle, and they are placed 

 from i to 2 cm. apart. According to Bernhardt the following distances of the 

 cylinders of the induction-apparatus represent the minima of sensation, and the 

 figures in parenthesis the minima of pain in a healthy person: tip of the tongue 

 17.5 (14.1) ; palate 16.7 (13.9) ; tip of the nose, eyelids, gums, back of the tongue, 

 red lips 15.7-15.1 (13-12.5); cheek, lips, forehead, 14.8-14.4 (13-12.5); acromion, 

 sternum, nape of the neck 13.7-13 (11.5-12.2); back of the arm, buttocks, occiput, 

 loin, neck, forearm, vertex, coccyx, thigh, back of the first phalanx, back of the 

 foot 12. 8-12 (12-9.2); back of the second phalanx, back of the metacarpal bone, 

 back of the hand, leg, distal phalanx, knee 11.7-11.3 (10.2-8.7); palmar aspect 

 of the head of the metacarpal bone, tip of the toe, palm of the hand, palmar 

 aspect of the second phalanx, hypothenar eminence, plantar aspect of the first 

 metatarsal bone, 10.9-10.2 (8-4). Motczutkowski found the pelvic region 

 the least sensitive to painful impressions, the sensitiveness increasing from this 

 situation in all directions. The ventral aspect of the body is less sensitive than 

 the lateral, and the latter less so than the dorsal. Those regions exhibit less 

 sensitiveness that have a thick epidermis; those that are less exposed to external 

 injuries and areas over joints and interosseous sutures exhibit increased sensitive- 

 ness. 



Pathological. When there is increased sensibility of the nerves transmitting 

 painful impressions even slight contact with the skin, or a mere breath of air 

 upon it, may cause the most violent pain (cutaneous hyperalgja), especially in 

 the presence of inflammatory or exanthematous conditions of the skin. The 



