ON THE MAMMALIAN NERVOUS SYSTEM. 285 



value of the cord excitatory effect direct and crossed when the cortex is excited, 



(2) the determination of the bilaterality of representation in one hemisphere, and 



(3) that of the extent to which fibres cross from one side of the cord to the other. 

 We therefore devised the plan of dividing the exposed portion of cord by a longi- 

 tudinal incision, either in the lateral or antero-posterior direction. 



The former was effected as follows : 



The cord, having been exposed, was severed, freed from its attachments, as previously 

 described, but not ligatured. It was then kept bathed with warm saline, and placed 

 upon a thin sheet of warmed cork with a shallow groove in it. The posterior fissure 

 could always be easily seen, and a longitudinal incision was then carried through it from 

 the posterior to the anterior fissure by means of a razor or sharp scalpel, the incision 

 commencing at the attached end of the cord. It is essential that in this operation 

 the instrument should neither pull nor press upon the cord unduly, but, since the 

 division involves both pressure and pull, the infliction of injury can only be miti- 

 gated by slowly making drawing incisions, first only through the posterior fissure, 

 and subsequently deeper and deeper until they have passed into the thickness 

 of the cord. The exposed portion is partly divided in this way down to its point of 

 transverse division for a distance of 2 centims. or more. Irrigation with warm saline 

 being maintained, the edges of the wound are gently separated, when the central 

 canal of the cord will be seen in the bottom of the cut ; with this as a guide, it is easy 

 to continue by similar incisions the mesial division, until a complete separation of the 

 cord into two halves is effected. (See Plates 31 and 33.) 



Each half thus prepared was now ligatured close to its cross section, and raised in 

 air for the necessary isolation when it was desired to subject them to electrical 

 observation. They were kept apart by the ligatures being carried to the respective 

 ends of a glass T-piece, or of two vulcanite rods arranged as a V. 



Frequently the cord, when thus prepared, bled rather freely from the central end 

 of the cut. 



The simplest way to check this was found to be to press into the lips of the cut a 

 small fragment of soft dry amadou, and leave it in contact with the bleeding point.! 



It might, perhaps, have been expected that such division would seriously impair 

 the physiological conduction of its fibres. It will be seen in the following pages that, 

 as far as the lateral tract is concerned, such impairment is not evidenced by our 

 observations, but that undoubtedly the posterior columns in the immediate neigh- 

 bourhood of the incision are injuriously affected by the process. 



We have also divided the cord into a posterior and anterior half by gently raising- 

 it when freed and passing through it a thin-bladed knife from side to side opposite the 

 attachment of the ligamentum denticulatum, and carrying it forward to the free end 

 of the preparation. 



