LATERAL SEMISECTION OF THE CORD. 86 1 



cephalic sense organs. Cerebral confluence of long-conduction arcs 

 seems of high importance in neural evolution. Complete transection of 

 the cord ruptures, of course, all these long-conducting paths for all 

 regions on the caudal side of the transection. After partial transections, 

 the motor and sentient state of the distal region gives information as to 

 the course that impulses must take. 



Lateral semisection of the cord. The results of semisection have 

 been studied at various levels of the cord. As regards the paths inter- 

 rupted, it is found that nerve fibres degenerate on the cephalic side 

 of the lesion in both the dorsal and ventro-lateral columns. The 

 degeneration in the former is completely homonymous, and extends up 

 to the bulb, reaching the dorsal column nuclei, Goll's only, if the semisec- 

 tion be not anterior to the thoracic levels ; both Goll's and Burdach's, if 

 the semisection be in the cervical region. 1 The number of degenerating 

 fibres gradually diminishes with increase of distance from the level of 

 transection, and as it is traced headwards concentrates toward the 

 median line. In the ventro-lateral column the degeneration im- 

 plicates fibres ascending to the superior vermis of the cerebellum 

 by the restiforin and retronexed conjunctival cerebellar tracts, and to 

 the mesencephalic roof and to the optic thalamus in lesser quantity. 2 

 The degeneration in the ventro-lateral column is heavier on the 

 homonymous side, but is not confined to it. From lesions low in 

 the thoracic region, ascending fibres degenerate in the ventral lip of 

 the column, which seem to end in the cervical region of the cord and 

 lower part of the bulb. 3 



Gotch and Horsley have examined the action currents 4 arising on 

 stimulation of the sciatic nerve, after semisection at the lower thoracic region, 

 and these are found to agree fairly with the data ascertained by degeneration. 

 Seventy-seven per cent, of the angular measure of the galvanometric de- 

 flection appeared to belong to the dorsal column. Of the remaining 23 

 per cent, rather less than four-fifths was referable to the rest of the homonymous 

 half of the cord. A discrepancy between the observations by the galvano- 

 metric and by the Wallerian method lies in the existence of action currents in 

 the contralateral dorsal column, to the extent of one-fourth of that observed in 

 the uncrossed, whereas no Wallerian degeneration occurs in the contralateral 

 dorsal column. The degeneration and the action current in the homonymous 

 dorsal column both conform with the course of the ascending stems of the dorsal 

 root fibres. After spinal semisection at the lower thoracic region, stimuli applied 

 to the skin of the foot are more effective for producing movement of the fore-limb 

 when applied to the foot homonymous with the lesion, than when contralateral. 

 There is no crossed path in the dorsal column at the level of semisection 

 to account for this, and it still occurs when much of the grey matter and 

 ventro-lateral column have been excluded. In the action-current observations 

 it was noticed that semisection at the bottom of the thoracic region reduced 

 the galvanometric deflection obtained from the cord a few segments higher 

 when the homonymous sciatic was faradised. Three observations were made ; 

 the reduction varied from 56 to 85 per cent, of the angular deflection. When 

 the crossed sciatic was faradised, the deflection in one of the observations was 

 somewhat greater than before the semisection, in the other two it fell to 63 

 and 90 per cent, of the previous angle. Most of this was probably referable 



1 Vide supra, p. 792. 2 Vide supra, p. 806. 



3 Sherrington, Journ. Physiol., Cambridge and London, 1893, vol. xvii. ; Laslett and 

 Warrington, Brain, London, 1899, vol. xxii. p. 586. 



4 Gotch and Horsley, Phil. Trans., London, 1891. 



