TRANSMISSION OF IMPULSES. 451 



others (Calmeil and Chauveau) have found these columns quite inexcita- 

 ble, and incapable of causing muscular contraction. But in such in- 

 stances experiments with a positive result are much more decisive than 

 those which are merely negative, since the natural excitability of the 

 anterior columns might be temporarily suspended by the operation of 

 opening the spinal canal, or other incidental conditions; but nothing 

 of this kind could confer upon them a property which they did not 

 naturally possess. 



Vulpian has shown 1 that, if in the living animal the spinal cord be 

 divided transversely, and both posterior and lateral columns, together 

 with the anterior and posterior nerve roots, separated from it for a 

 distance of four or five centimetres below the point of section, leaving 

 this portion of the cord to consist of the anterior columns and the 

 gray substance only, irritation of the anterior columns, thus isolated, 

 will still produce convulsive movement in the parts below. 



There can be no doubt, accordingly, of the excitability of the anterior 

 columns. This excitability, which produces simple convulsive move- 

 ments in the parts below, is also in most instances unaccompanied by 

 pain or other evidences of sensibility. The absence of pain, in cases 

 where the convulsive action is well marked, has been especially noticed 

 by Flint, 2 and is also mentioned by various other writers. 



The sensibility of these parts which has sometimes been observed is 

 comparatively slight in degree, and is frequently altogether suspended 

 or abolished by the opening of the vertebral canal and the exposure of 

 the spinal cord. 



The lateral columns are also excitable in their anterior portions, near 

 the attachment of the anterior nerve roots ; while as we approach their 

 posterior portions, this direct excitability, according to Vulpian, dimin- 

 ishes in degree, and gradually gives place to the phenomena of sensi- 

 bility characteristic of the posterior parts of the cord. 



The anterior, lateral, and posterior columns of the cord are not there- 

 fore absolutely limited and distinguished from each other by their 

 physiological properties. The fibres of the anterior and posterior nerve 

 roots pass in horizontally between the longitudinal fibres of the adjacent 

 columns ; but both the anterior and lateral columns, on each side of the 

 anterior nerve roots, are excitable and produce movement on being irri- 

 tated, and both the posterior and lateral columns, near the entrance of 

 the posterior nerve roots, are endowed with sensibility. Inflamma- 

 tory or other irritation of the meninges, over any part of the anterior 

 aspect of the cord, may accordingly cause convulsive movements in the 

 regions situated below the diseased point ; and it is possible that either 

 pain alone or convulsions alone may be the symptoms of inflammatory 

 irritation of the posterior or anterior portions of the cord respectively. 

 But it is most frequently the case that the morbid action extends more 



1 Systeme Nerveux. Paris, 1866, p. 360. 



2 Physiology of Man ; Nervous System. New York, 1872, p. 276. 



