458 



MESSRS. F. GOTCH AND V. HORSLEY 



AVERAGE Nerve Effect produced by Cord Excitation (Cat and Monkey). 



The sum of the average effects produced by all the columns is 110; of this the 

 posterior column on the side of the nerve is capable of evoking about 73 per cent., 

 the posterior column of the opposite side 15 per cent., the lateral column of the same 

 side 9 per cent., and the lateral column of the opposite side 3 per cent. 



There is a great similarity, at least as regards the relation of the crossed to the 

 uncrossed side, between these different quantities and those which were referred to at 

 the end of the nerve-to-cord experiments, detailed in Chapter IX. An exact similarity 

 could not be expected, since we are dealing in the present case with mixed nerves, 

 hence efferent as well as afferent fibres are the subject of observation. 



The presence of impulses which may be supposed to emerge from the cord by the 

 anterior roots might account for an increase in the effect evoked in the nerves, since 

 the excitation of such columns as the posterior may awaken reflex discharges from 

 the cord down the motor roots. 



This explanation, however, cannot be applied to the effects evoked by excitation of 

 the lateral column on the side of the nerve, since we see that the effect evoked by 

 this column is smaller than that which the results of Chapter IX. would lead us to 

 expect as probable from the indirect connections of its fibres with those of the 

 posterior root only. There is no evidence of any accession of nerve impulses through 

 this excitation, but rather of a resistance to the passage of impulses from the cord 

 through the lateral indirect path into the fibres of the mixed nerve. 



It is, however, essential to ascertain the amount of the effects in the afferent and 

 efferent nerve tracts before proceeding to discuss in more detail what the above 

 experiments seem to indicate as to the relations of the cord to its nerves. 



SECTION 4. THE ELECTRICAL EFFECTS IN AFFERENT NERVES FOLLOWING EXCITATION 

 OF THE SPINAL CORD ABOVE THEIR POINT OF ENTRY. 



(1.) Tlie Posterior Roots. 



The simplest mode of obtaining the effects in afferent nerves is that of exposing a 

 posterior root, dividing it near the ganglion and connecting its cut central end and 



