PATHS OF CONDUCTION IN THE COED. 595 



In some experiments made in 1863 (Flint) upon a living dog, the cord 

 having been exposed in the lumbar region and stimulated mechanically and 

 with an electric current two hours after the operation, certain positive results 

 were obtained, which led to the following conclusions : 



The gray substance is probably inexcitable and insensible under direct 

 stimulation. 



The antero-lateral columns are insensible, but are excitable both on the* 

 surface and in their substance ; and direct stimulation of these columns pro- 

 duces convulsive movements in certain muscles, which movements are not 

 reflex and are not attended with pain. The lateral columns are less excitable 

 than the anterior columns. 



The surface, at least, of the posterior columns is very sensitive, especially 

 near the posterior roots of the nerves. The deep portions of the posterior 

 columns are probably insensible, except very near the origin of the nerves. 



The above conclusions refer only to the general properties of different 

 portions of the cord, as shown by direct stimulation, in the same way that 

 the general properties of the nerves in their course are demonstrated. 



Motor Paths in the Cord. What has been said regarding the direction 

 of the fibres in the cord and the situation and course of the degenerations 

 following destruction of motor cerebral centres conveys a definite idea of the 

 motor paths in the cord. This idea is sustained by experiments in which 

 different columns of the cord have been divided in living animals. 



The motor paths are in the direct pyramidal tracts (columns of Tiirck) 

 and in the crossed pyramidal tracts of the lateral columns. The motor im- 

 pulses are conveyed by the fibres of these tracts to the multipolar cells in the 

 anterior cornua of gray matter and are thence transmitted to the anterior 

 roots of certain spinal nerves. In the lower dorsal region the conduction 

 is confined to the crossed pyramidal tracts in the lateral columns, while 

 above, the direct pyramidal tracts participate in this action. 



The motor fibres decussate in the anterior pyramids of the medulla oblon- 

 gata (crossed pyramidal tracts), and in the cervical region, to a comparatively 

 slight extent, before the direct pyramidal tracts (columns of Tiirck) pass to 

 the encephalon. In the cervical region the decussation takes place probably 

 in the anterior white commissure. The fact of this decussation of motor 

 conductors is sustained by pathology paralysis of motion following brain- 

 lesions, occurring on the opposite side of the body and by experiments in 

 which the fibres as they cross are divided by a longitudinal median section 

 in the medulla and in the cervical region of the cord. 



Vaso-motor nerve-fibres exist in the lateral columns of the cord and 

 probably are connected with the cells of the gray matter. They pass out in 

 the anterior roots of the spinal nerves and go to the blood-vessels either 

 from the branches of the spinal nerves directly or through filaments sent to 

 the sympathetic. 



Sensory Paths in the Cord. The gray matter of the cord is the part 

 concerned in the conduction of sensory impressions (Bellingeri, 1823). This 

 fact has been verified by recent experiments ; but it is thought that some of 



