ANATOMY AND PHYSIOLOGY OF THE SPINAL CORD. 405 



nervous centre, is in itself entirely independent of the will, 

 and consists in the reception of an impression through the 

 sensory nerves, and the consequent generation of nervous 

 force to be transmitted through the motor trunks. Accord- 

 ing to Van der Kolk, the transmission is effected through 

 the ganglionic cells in the superior horn of grey matter, 

 and the fibres which connect these with the motor cells 

 in the inferior horn ; nervous force is generated in the 

 latter, and conveyed along the motor nerves. Each group 

 of cells in the anterior horns is understood to preside over 

 a distinct muscle, or over several which act in unison, so 

 that the application of a stimulus to a group leads to a 

 natural and harmonious action. The groups being con- 

 nected somewhat less intimately with each other, a more 

 powerful impression leads to a simultaneous emission of 

 force by two or more adjacent to each other, and to 

 a mo-re extensive though still natural movement. More- 

 over, the cells in the two lateral halves of the cord are 

 connected in an analogous way, and accordingly reflex 

 movements on the two sides simultaneously are by no 

 means uncommon. 



One of the most remarkable instances of this latter 

 movement is in the case of the decapitated frog. He will 

 remain quite still until an irritant is applied to some part 

 of the body, when, if not severe, a foot may be mechanically 

 raised to remove it ; if, on the other hand, an active irritation 

 is made, the reflex movement will be much more extensive, 

 and may even go the length of a leap. An instance almost 

 quite as remarkable is that in which, from disease or injury 

 of the spinal cord, its lower portion is cut off from all com- 

 munication with the brain. No pinching or injury of the 

 lower limbs can be felt, and no effort of the will can effect 

 their movement ; yet, by tickling the sole of a foot, a 



