CONDUCTING PATHWAYS IN THE SPINAL CORD 597 



logical anatomy has shown that the seat of this disease is in the posterior 

 columns, exclusive of their ventral sections. Hence we can say that the tracts 

 for motor sensations in part, at least, traverse the posterior columns. These 

 tracts are on the homonymous side of the cord, substitution of the other side 

 appearing very tardily if at all. 



In the dog, after section of the posterior columns, not only does the sensa- 

 tion of pain persist, but likewise the coarser sensations of touch and position as 

 well as a crude power of localization. There is no apparent interference with 

 walking nor with finer isolated movements (Borchert). 



How the different sensory impressions received by the skin are propagated 

 through the spinal cord is a much more difficult question. 



The original doctrine of Brown-Sequard that these sensations traverse 

 only the heteronymous side of the cord has been both confirmed and denied 

 by many authors. We shall limit ourselves here to the view of Kocner, who 

 has made an exhaustive study based on abundant clinical material of his own. 

 According to this author, a hemilesion of the spinal cord produces on the 

 injured side hypercesthesia for touch and pain, and in many cases also for 

 heat and cold. Even the deeper parts are included in this change, so that 

 movements of the limbs become very painful. On the opposite side there 

 is, as a rule, a reduction of sensibility. But it varies both as to intensity and 

 quality according to the extent of the injury. Either every kind of sensation 

 is lost altogether or, as is very often the case, the sensation of touch remains 

 intact while the others are lost, or, finally, the sensation of pain is merely 

 blunted and the sensations of heat and cold are lost. 



However, these disturbances are not final on either side. The hyperas- 

 thesia on the injured side declines and the loss of sensation on the opposite 

 side gradually disappears, though for a long time it requires a stronger stimu- 

 lus to produce the sensation which has been affected. The return of pain 

 sensations may precede the revival of touch, the latter that of heat, and heat 

 that of cold. These 1 variations of the symptoms are referable to differences 

 in the extent of the lesion. 



After an exhaustive discussion of the clinical observations, Petren has 

 reached the following conclusions with regard to the tracts of the cord in 

 which the different cutaneous sensations are propagated. The pressure sense 

 is mediated by two different tracts: the one ascends in the posterior columns 

 of the same side and is the direct continuation of the posterior roots; the 

 other, after entering by the posterior horn, crosses entirely to the opposite 

 side and ascends probably as a part of Gowers's tract (cf. Fig. 264) in the 

 lateral column. The tracts for pain and temperature sensations follow this 

 second tract for pressure, hence run in the cord only on the opposite side from 

 the place in the skin where they originate. 



EEFERENCES. L. F. Barker, " The Nervous System," New York, 1899. 

 W. v. Bechterew, " Die Leitungsbahnen im Gehirn und Riickenmark," second 

 edition, Leipzic, 1898. Bethe, " Allgemeine Anatomie und Physiologie des 

 Nervensystems," Leipzic, 1903. L. Edinger, " Vorlesungen iiber den Bau der 

 nervosen Zentralorgane," seventh edition, Leipzic, 1904. Exner, " Entwurf zu 



