392 THE NERVOUS SYSTEM. 



cord. The irritation thus produced is still more liable to cause pain, on 

 account of the attachment at the surface of the cord of the posterior 

 nerve roots, which are themselves acutely sensitive. 



The properties shown by the anterior columns on the application of 

 artificial stimulus are, on the whole, quite different from those of the 

 posterior columns. There is some difference in the results obtained 

 in this respect by experimenters. This difference mainly consists in 

 the fact that, according to the large majority (Magendie, Longet, 

 Bernard, Brown-Sequard, Vulpian, Flint), irritation of the anterior 

 columns produces convulsive movement in the parts below ; while others 

 (Calmeil and Chauveau) have found these columns inexcitable. But 

 in such instances experiments with a positive result are more decisive 

 than those which are negative, since the excitability of the anterior 

 columns might be suspended by opening the spinal cord, or by other 

 incidental conditions ; but nothing of this kind could confer upon them 

 a property which they did not naturally possess. 



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

 columns. This excitability, while producing convulsive movements in 

 the parts below, is in most instances unaccompanied by sensibility. 

 The absence of pain, in cases where the convulsive action is well 

 marked, has been especially noticed by Flint,* and is mentioned by 

 various other writers. 



The sensibility of these parts, sometimes observed, is slight in degree, 

 and is frequently suspended or abolished by exposure of the spinal 

 cord. 



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

 the anterior nerve roots ; while toward their posterior portions, accord- 

 ing to Yulpian, the excitability diminishes, and gradually gives place 

 to the phenomena of sensibility characteristic of the posterior parts of 

 the cord. 



The anterior and posterior portions of the 'cord are therefore distin- 

 guished, in great measure, by their mode of reaction toward external 

 irritation. The anterior and lateral columns, on each side of the ante- 

 rior 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. Inflammatory 

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

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

 limbs below ; and either pain alone or convulsions alone may be the 

 symptoms of inflammatory irritation of the posterior or anterior por- 

 tions of the cord respectively. But the morbid action most frequently 

 extends to both regions, and disturbances of sensibility and motion are 

 present at the same time, or at different periods in the disease. 



II. What parts of the Spinal Cord are the natural channels for 

 sensation and movement ? 



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



