SENSOKY CONDUCTION IN THE SPINAL CORD. 255 



dorso-lumbar region ; that partial decussation occurs in the 

 cervical region ; and that 1 the decussation is completed in 

 the anterior pyramids of the medulla oblongata. 



Transmission of Sensory Impressions in the Cord. 

 There is very little room for discussion concerning what is 

 positively known with regard to the transmission of sensory 

 impressions in the cord, though there are some portions of 

 its structure, the action of which in conduction is still ob- 

 scure. Early in the physiological history of this portion of 

 the nervous system, Longet made a number of experiments, 

 which seemed to show that the posterior columns of the cord 

 were the conductors of sensory impressions to the brain, and 

 that the antero-lateral columns transmitted the motor stim- 

 ulus. These have been already referred to in connection 

 with the properties of the cord. They were made by apply- 

 ing a stimulus directly to the cord itself. Longet discredited 

 observations made by dividing different portions of the cord, 

 for the reason that he supposed that the mere operation of 

 exposing the cord and of removing the dura mater was 

 followed by a depression of the nervous action sufficient to 

 render the evidences of sensibility in the lower extremities 

 scarcely appreciable. 1 The conclusions drawn from these 

 experiments were at first accepted by nearly all physiologi- 

 cal writers, and it was generally admitted that the transmis- 

 sion of sensory impressions was effected solely by the pos- 

 terior columns. It was found that the gray matter of the 

 cord was both insensible and inexcitable, and the conduction 

 was supposed to take place exclusively through the white 

 substance. The views of Longet were in direct opposition 

 to those of Bellingeri, who claimed, in 1823, to have demon- 

 strated by experiment, that sensory impressions were con- 

 veyed to the brain exclusively by the gray substance of 

 the cord, and that sensibility persisted in the lower ex- 



1 LONGET, Anatomic et physiologic du tysteme nerveux, Paris, 1842, tome i., 

 p. 276. 



