SPECIAL PHYSIOLOGY. 45 



electricity to these columns ; more recently Fick has arrived 

 at similar results, and, moreover, has found that these columns 

 respond to mechanical irritations (pinching or bruising). We 

 shall conclude, then, as has this last-named experimenter, 

 that the excitability of the white anterior columns is real, 

 though less intense than that of the corresponding roots; 

 destined to transmit the commands of volition, these cerebro- 

 spinal commissures are not set in action except under the 

 influence of mechanical agents of sufficient energy. 2d. All 

 physiologists from the time of Magendie recognize that the 

 posterior columns are directly excitable by irritants more or 

 less slight, and then originate painful sensations. Movements 

 of a reflex character are likewise produced. 3d. Finally, in 

 order no longer to revert to these facts of excitability, let us 

 remark that the gray axis of the spinal cord is universally 

 recognized as inexcitable. 



The decussation (crossing over) of the columns of the spinal 

 cord, now perhaps admitted as a general fact, has been for a 

 long time suspected (Galen). Experiment has shown that 

 this decussation occurs in the different columns as well as 

 in different parts of the same column at various points: 

 1st, the antero-lateral column is but little, if at all, the 

 seat of decussation throughout the length of the spinal 

 cord properly so called ; this decussation occurs at the 

 point of the bulb (decussation of the pyramids), but in 

 the innermost band of the anterior columns there is none ; 

 the decussation of this column occurs higher up : in every case 

 there is found in front of the protuberance new decussations 

 of fibres, and especially nerve fibres that go from the brain 

 to the roots of the nerves of that region (facial, motores 

 oculorum) ; in treatises on pathology it will be remarked how 

 a knowledge of these decussations are an important -means of 

 explaining paralyses on the side of the face and extremities op- 

 posite the lesion (Gubler). 2d. According to the majority of 

 physiologists, the posterior columns decussate throughout the 

 length of the spinal cord, in such wise that the unilateral 

 lesions of the spinal cord destroy sensibility on the opposite 

 side and motility on the same side as that in which they 

 occur. 3d. Finally, in the gray substance, which also serves 

 as a conductor, there seems to be a decussation, but here the 

 facts are less distinct ; the transmission of sensibility appears 

 in every way, for if two transverse semi-sections are made at 

 different heights of the spinal cord, the transmission of periph- 

 eral (or outward) impressions is not interrupted; provided 



