ON THE MAMMALIAN NERVOUS SYSTEM. 407 



IV. The table just given indicates that the indirect path along which impulses are 

 conducted from the excited end is not confined to the column, and suggests that the 

 size of the effect evoked indicates the amount of indirect connection through cells with 

 other columns. 



V. The magnitude of the indirect .effect evoked is greatest in the case of the 

 lumbar excitation of the posterior columns ; the afferent indirect connections leading 

 upwards from this column are, therefore, either very numerous or offer little resistance, 

 and spread largely into other regions. 



VT. The effect is still comparatively large when evoked by dorsal excitation of the 

 interrupted posterior column. There are, therefore, indirect connections leading 

 downwards towards the periphery, possibly the same to some extent as those just 

 mentioned in V., but either less numerous or offering more resistance, or spreading to 

 a less extent into other regions. 



VII. The excitation of the dorsal end of the interrupted lateral column evokes 

 electrical effects, hence indirect connections are thereby suggested spreading from the 

 lateral column downwards into other regions ; these, however, are leas numerous or 

 offer more resistance than those mentioned in VI. 



VIII. The excitation of the lumbar end of the interrupted lateral column evokes 

 no effect, hence all the channels in this column, by which impulses could pass 

 upwards, are absolutely confined to the column. 



IX. The striking feature of the preceding conclusions is that the connections of 

 the fibres of the posterior columns are framed on a different plan from those of the 

 laterals. The posterior column fibres spread into other columns both as they ascend 

 and to a less degree as they descend ; the lateral fibres, however, spread into other 

 columns particularly as they descend. The posterior columns offer thus special 

 facilities for conveyance and distribution of afferent impulses ; the lateral special 

 facilities for the conveyance and distribution of efferent impulses. 



It will be remarked that the conclusions just suggested as to the relations of the 

 columns are in accordance with the views of SCHIFF, " die Hinterstrange bis ins Hirn 

 hinein bilden die Legislative, die Turck'schen Biindel erwecken die Exekutive." 



In conclusion, we draw attention to the general indications as to the structure of 

 the cord which the whole of these experiments imply. 



Since the electrical effect obtained by the " minimal" stimulation of the cut end of 

 one column is apparently due to the excitation of the direct fibres in that column 

 only, the average amounts obtained in the case of the different columns is related 

 to the excitability and number of the fibres contained. As regards the excitability 

 of the direct fibres in different columns, there is no reason for supposing that these 

 direct fibres, which have no connection with cells between the two ends of the experi- 

 mental tract, are in any marked degree more excitable in one column than in another. 

 The amount of the " minimal " effect must therefore depend upon the number of fibres 



