47C MESSRS. F. GOTCH AND V. HORSLEY 



If these results are to be relied upon as indicating not merely different amounts of 

 electrical change, but the presence of different amounts of nerve impulses propagated 

 from the stimulated area along the cord and into the observed nerve, then their main 

 features indicate the following relations between the dorsal cord and the sciatic 

 nerve in the case of cord-to-nerve, experiments: 



(1.) The path of least resistance, as shown by "minimal" stimulation, between the 

 cord and the afferent fibres of the sciatic nerve, is that of the posterior column of 

 the same side ; this path being that of the directly continuous afferent fibres. 



(2.) Of the indirect nerve paths between the cord and the afferent fibres, the path 

 of least resistance is that of the posterior column of the opposite side, as is shown 

 also by Table II. 



(3.) The afferent paths, direct and indirect, along which nerve impulses can be made 

 to travel (backward) from the stimulated cord to the sciatic nerve, have the following 

 relations to the posterior roots of the sciatic nerve, as shown in Table I: 



(a.) The posterior column of the same side conveys 77 per cent, of the amount of 

 nerve impulses ; 



(b.) The lateral column of the same side conveys 7 per cent. ; 



(c.) The posterior column of the opposite side conveys 15 per cent. ; 



(d.) The lateral column of the opposite side conveys a mere trace. 



We will now compare these deductions with those of the preceding chapter from 

 nerve-to-cord experiments. These latter were briefly as follows : 



(1.) The spinal path by which afferent impulses proceeding up the nerve travel in the 

 cord is, when these impulses are generated by " minimal " excitation, almost entirely 

 that of the posterior column of the same side, i.e., the directly continuous one. 



(2.) Of the indirect spinal paths along which such ascending impulses travel, that in 

 the lateral column is the path of least resistance of the same side. 



(3.) All the afferent spinal paths have the following relations to the posterior roots of 

 the sciatic nerves as regards the transmission of afferent impulses generated in the 

 fibres of the sciatic nerve : 



(a.) The posterior column of the same side conveys an average of 60 per cent, of 

 the total amount (intensity and quantity) of nerve impulses ; 



(b.) The lateral column of the same side conveys 20 per cent. ; 



(c.) The posterior column of the opposite side conveys 15 per cent. ; 



(d.) The lateral column of the opposite side conveys 5 per cent. 



The following features of these two sets of deductions are similar : 



i. That the channel of connection with the posterior roots is par excellence that o 7 * 

 the fibres in the posterior column of the same side ; 



ii. That what crossing does exist is almost entirely due to indirect continuity with 

 the fibres in the posterior column of the opposite side ; 

 / iii. That the crossed path represents only about 15 per cent, of the available path ; 



iv. That the fibres in the lateral column have very much closer indirect relations 



