278 NERVOUS SYSTEM. 



columns are not excitable, even near the roots of the nerves ; 

 and that when convulsive movements follow galvanization 

 near the roots, this is due to an extension of the current to 

 the roots themselves. 1 



As the result of the most definite and reliable experi- 

 ments of others, bearing upon the question of the properties 

 of the cord, and of our own observations, we have arrived 

 at the following conclusions : 



The gray substance is probably inexcitable and insensible 

 under direct stimulation. 



The antero-lateral columns are insensible, but are excita- 

 ble both on the surface and in their substance ; i. e., direct 

 stimulation will produce convulsive movements in certain 

 muscles, which movements are not reflex and are not attend- 

 ed 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 in- 

 sensible, except very near the origin of the nerves. 



The above conclusions refer only to the general proper- 

 ties of different portions of the cord, as shown by direct 

 stimulation, in the same way that we demonstrate the gen- 

 eral properties of the nerves in their course. In all proba- 

 bility, the fibres in the white and gray substance of the cen- 

 tral nervous system conduct motor stimulus from the brain 

 and sensory impressions to the brain, while they are them- 

 selves insensible and inexcitable under direct stimulation. 

 The physiological action of the cord as a conductor, one of 

 the most interesting and important of its functions, will be 

 fully considered in another chapter. 



1 HUIZINGA, Die Unerregbarkeit der vorderen RucJcenmarkstrange.Archiv 

 fur die gesammte Physiologic, Bonn, 1870, Bd. Hi., S. 81, et seq. 



