646 HYPERESTHESIA. 



any transverse section of the cord constricts all the blood-vessels below the point of 

 section (C. Ludwiff and Thiry). In the same way, the fibres which ascend in the 

 cord, and increase the action of the vaso-motor centre pressor fibres, are also 

 excitable (C. Ludxvig and Dittmar% 364, 10). Stimulation of these fibres, 

 although* it affects the vaso-motor centre reflexly, does not cause sensation. 



4. Chemical stimuli such as the application of common salt, or wetting the 

 cut surface with blood, appear to excite the spinal cord. 



5. The motor centres are directly excited by blood heated above 40 C, or by 

 asphyxiated blood, or by sudden and complete anaemia of the cord produced by 

 ligature of the aorta (Sigm. Mayer) ;! and also by certain poisons picrotoxin, 

 uicotin, and compounds of barium (Luchsinger). 



Action of Blood and Poisons. In experiments of this kind, the spinal cord ought to be 

 divided at the 1st lumbar vertebra, at least twenty hours before the experiment is begun. It is 

 well to divide the posterior roots beforehand to avoid reflex movements. If, in a cat thus 

 operated on, dyspnan be produced, or its blood overheated, then spasms, contraction of the vessels, 

 and sccrctian of sweat occur in the hind limbs, together with evacuation of the contents of 

 the bladder and rectum, while there are movements of the uterus and the vas deferens. Some 

 poisons act in a similar manner. In animals with the medulla oblongata divided, rhythmical 

 respiratory movements may be produced if the spinal cord has been previously rendered very 

 sensitive by strychnin or overheated blood (P. v. Rokitansky, v. Schroff% 368). 



The ganglion-cells of the anterior cornu can be excited mechanically (Birge), 

 and, according to Biedermann, the grey matter also responds to electrical stimuli. 



Hyperesthesia. After unilateral section of the cord, or even only of the 

 posterior or lateral columns, there is hyperesthesia on the same side below the 

 point of section (Fodera, 1823, and others), so that rabbits shriek on the slightest 

 touch. The phenomenon may last for three weeks, and then give place to normal 

 or sub-normal excitability. On the sound side the sensibility remains permanently 

 diminished. A similar result has been observed in cases of injury in man. An 

 analogous phenomenon, or a tendency to contraction in the muscles below the 

 section (hyperkinesia), has been observed by Brown-Sequard after section of the 

 anterior columns. 



The excitability of the cord is intimately dependent on the continuance of the 

 circulation, for ligature of the abdominal aorta rapidly paralyses the lower 

 extremities (Slenson, 1667), due to anaemia of the cord (Schife?*). Later, the 

 anterior roots of the spinal nerves, and the anaemic part of the grey matter of the 

 cord, undergo degeneration. 



364. THE CONDUCTING PATHS IN THE SPINAL CORD. [Posterior 

 Root. (a) The inner part, or internal radicular fasciculus is supposed to convey 

 the impressions from tendons and those for touch and locality. When the postero- 

 external column is diseased, as in locomotor ataxia, the deep reflexes, especially the 

 patellar tendon reflex, are enfeebled, or it may be abolished, while the implication 

 of the fibres of the internal fasciculus gives rise to severe pain, (b) The outer 

 radicular fibres enter the grey matter of the posterior horn, and are supposed to 

 convey the impressions for cutaneous reflexes and temperature, (c) The central 

 fibres pass directly into the grey matter, and are supposed to conduct painful 

 impressions into the grey matter (fig. 449).] 



1. Localised tactile sensations (temperature, pressure, and the muscular sense 

 impressions) are conducted upwards through the posterior roots to the ganglia of 

 the posterior cornu, and lastly into the posterior column of the same side. 



In man, the conducting path from the legs runs in Goll's column, while those for the arms 

 run in the ground-bundle (fig. 454) {Flechsig). In rabbits, the path of localised tactile impres- 

 sions lies in the lower dorsal region in the lateral columns (Ludwig and Woroschiloff, Ott and 

 Meade-Smith ). 



Anesthesia. Section of individual parts of the lateral columns abolishes the sensibility for 

 the parts of the skin connected with the part destroyed, while total section produces the same 



