CONDUCTING PATHS IN SPINAL CORD. 647 



result for the whole of the opposite side of the body below the section. The condition where 

 tactile and muscular sensibility is lost is known as anaesthesia. 



2. Localised voluntary movements in man are conducted on the same side 

 through the anterior and lateral columns ( 358 and 365), in the parts known as the 

 pyramidal tracts. The impulses then pass into the cells of the anterior cornu, and 

 thence to the corresponding anterior nerve-roots to the muscles. The exact section 

 experiments of Ludwig and Woroschiloff showed that, in the lower dorsal region of 

 the rabbit, these paths were confined to the lateral columns. Every motor nerve- 

 fibre is connected with a nerve-cell in the anterior horn of the frog's spinal cord 

 (Gaule and Birge). Section of one lateral column abolishes voluntary movement 

 in the corresponding individual muscles below the point of section. It is obvious, 

 from the conduction in 1 and 2, that the lateral columns must increase in thickness 

 and number of fibres from below upwards (Stilling, Woroschiloff) [see fig. 443]. 



3. Tactile reflexes (extensive and co-ordinated). The fibres enter by the 

 posterior root, and proceed to the posterior cornu. The groups of ganglionic cells, 

 which control the co-ordinated reflexes, are connected together by fibres which run 

 in the anterior tracts, the anterior ground bundle and (1) the direct cerebellar tracts 

 (p. 633). The fibres for the muscles which are contracted pass from the motor 

 ganglia outwards through the anterior roots. 



In ataxic tabes dorsalis, or locomotor ataxia, there is a degeneration of the posterior columns, 

 characterised by a peculiar motor disturbance. The voluntary movements can be executed with 

 full and normal vigour, but the finer harmonious adjustments are wanting or impaired, both in 

 intensity and extent. These depend in part upon the normal existence of tactile and muscular 

 impressions, whose channels "lie in the posterior columns. After degeneration of the latter, 

 there is not only anaesthesia, but also a disturbance in the discharge of tactile reflexes, for which 

 the centripetal arc is interrupted. But a simultaneous lesion of the sensory nerves alone may 

 in a similar manner materially influence the harmony of the movements, owing to the analgesia 

 and the disappearance of the pathic reflexes ( 355). As the fibres of the posterior root traverse 

 the white posterior columns, we can account for the disturbances of sensation which characterise 

 the degenerations of these parts (Charcot and Pierret). But even the posterior roots themselves 

 may undergo degeneration, and this may also give rise to disturbances of sensation (p. 618). 

 The sensory disturbances usually consist in an abnormal increase of the tactile or painful sensa- 

 tions, with lightning pains shooting down the limbs, and this condition may lead to one 

 where the tactile and painful sensations are abolished. At the same time, owing to stimu- 

 lation of the posterior columns, the tactile sensibility is altered, giving rise to the sensation of 

 formication, or a feeling of constriction ["girdle sensation"]. The conduction of sensory 

 impressions is often slowed ( 337). The sensibility of the muscles, joints, and internal parts 

 is altered. 



The maintenance of the equilibrium is largely guided by the impulses which travel inwards 

 to the co-ordinating centres through the sensory nerves, special and general, deep and super- 

 ficial. In many cases of locomotor ataxia, if the patient place his feet close together and close 

 his eyes, he sways from side to side and may fall over, because by cutting off the guiding 

 sensations obtained through the optic nerve, the other enfeebled impulses obtained from the 

 skin and the deeper structures are too feeble to excite proper co-ordination. 



4. The inhibition of tactile reflexes occurs through the anterior columns ; the 

 impulses pass from the anterior column at the corresponding level into the grey 

 matter, where they form connections with the reflex conducting apparatus. 



5. The conduction of painful impressions occurs through the posterior roots, and 

 thence through the whole of the grey matter. There is a partial decussation of 

 these impulses in the cord, the conducting fibres passing from one side to the other. 

 The further course of these fibres to the brain is given in 365. 



If all the grey matter be divided, except a small connecting portion, this is sufficient to 

 conduct painful impressions. In this case, however, the conduction is slower (Schiff). Only 

 when the grey matter is completely divided, is the conduction of painful impressions from below 

 completely interrupted. This gives rise to the condition of analgesia, in which, when the 

 posterior columns are still intact, tactile impressions are still conducted. This condition is 

 sometimes observed in man during incomplete narcosis from chloroform and morphia (Thiersch). 

 Those poisons act sooner on the nerves which administer to painful sensations than on those 

 for tactile impressions, so that the person operated on is conscious of the contact of a knife, but 



