934 



COMMON SENSATION. PAIN. 



sense the sensation of three points when only two are in contact with the skin, 

 or of two when only one is applied. The author observed in himself as a peculiar 

 paradoxical localization of sensation that pressure with the edge of the finger- 

 nail over the junction of the manubrium with the body of the sternum always 

 caused a sense of pricking in the chin. In this case irritation of one of the terminal 

 branches of the subcutaneous nerves of the neck is referred to the periphery of 

 another branch of the same nerve. A similar phenomenon is observed in other 

 nervous territories, especially where exact localization is rarely or never attempted. 

 The latter is the case with the sensory nerves of the intestines. Hence, it is not 

 astonishing that in the presence of painful affections of the intestines, pains 

 appear in distant parts of the skin supplied by nerves from the same level of the 

 spinal cord into which also the sensory visceral nerve enters. In the same category 

 is the familiar occurrence of pains in the left arm in connection with heart-disease. 

 Analogous conditions prevail in the head and the neck. A remarkable alteration 

 of the spatial sense consists in the circumstance that, when the eyes are closed, 

 the individual feels his body to be abnormally large, or greatly reduced in size, 

 or at times has a sensation of the trunk being doubled. The author has observed 

 the first condition also in connection with moderate morphin -intoxication. In 

 cases of degeneration of the posterior columns of the spinal cord Obersteiner 

 observed that the patient was uncertain whether he was touched on the right or 

 the left side (allocniria) . Brown-Sequard observed after section of a lateral half 

 of the cord that irritants applied to the left side were felt on the right side, and 

 conversely. Rarely in cases of brain-disease irritation applied to both sides of 

 the body has been felt only on one side. 



Impairment of tactile sensibility to the point of abolition (hypopselaphesia 

 and apselaphesid) may be present in association with corresponding disorders 

 of the sensory nerves or occur independently. Less commonly individual qualities 

 of the tactile sensations are lost, for example the pressure-sense, or the tempera- 

 ture-sense, or only sensibility for heat and cold, conditions that have been desig- 

 nated partial paralysis of the tactile sense. Limbs that are sound asleep, and are 

 insensitive to slight pressure-irritations, do not appreciate cold; the function of 

 the pressure-fibers and the heat-fibers is not disturbed until much later. 



COMMON SENSATION. PAIN. 



By common sensations are understood pleasant or unpleasant sen- 

 sations in parts of the body endowed with feeling, which are not 

 referable to external objects, and which in their peculiarity can be 

 neither described nor compared with other sensations. These include 

 pain, hunger, thirst, disgust, fatigue, horror, vertigo, tickling, sensuality, 

 comfort and discomfort, and the respiratory sensations of free or em- 

 barrassed breathing. 



Pain can appear wherever sensory nerves are present. The 

 organs subserving this sensation appear to be the free interepithelial 

 nerve-endings. The pain -points do not coincide, in general, with the 

 pressure -points, and they are about 1000 times less sensitive than the 

 latter. The cause of the pain is always an irritation of the sensory 

 nerves exceeding the normal. All kinds of irritation: mechanical, 

 thermal, chemical, electrical, and somatic (inflammatory processes, 

 disturbances of nutrition and the like) may excite pain. Especially 

 the last named appear to be particularly effective, as some tissues 

 are exceedingly painful when inflamed (for example muscles and bones), 

 while they are comparatively insensitive when incised. Pain may 

 be excited throughout the entire course of a sensory nerve, from its 

 center to the periphery, but the sensation is invariably referred to the 

 peripheral extremity, in accordance with the law of peripheral reference. 

 Inus, it may happen that irritation of the nerves, as in the scar of an 

 amputation-stump, may cause pain that is referred to parts that have 

 been long since removed. As a result of frequent irritation in the 



