434 MESSRS. F. GOTCH AXD V HORSLEY 



section of the part of the cord ventral to the posterior columns was made. The cord 

 was prepared in a Cat by division at the 8th dorsal vertebra ; the upper end of the 

 lower fragment connected with the galvanometer, and the left sciatic stimulated with 

 three different strengths of stimulus, and the effect noted in each case. An inter 

 vening section was then made at the 10th dorsal, so as to divide the whole region of 

 the coed Iving ventrally to the posterior commissure and the commissure itself, the 

 result being that the minimal effect remained unaltered, whereas the other effects 

 were diminished in the ratio of 100 to 76, as indicated in the subjoined table. 



: Efrect after 



section. 



35 35 



R&tio 100 to 76. 



This experiment, whilst it establishes the importance of the posterior columns by 

 furnishing the control experiment of leaving these tracts and excluding the others, is 

 at the same time a remarkable instance of the quantitative precision of the method, 

 since in independent experiments lesions effected quite differently show in the one 

 case that the posterior columns are concerned with 7S per cent., in the other with 

 76 per cent, of the effect. As the experimental details accumulate, this steady 

 quantitative relation wifl be found to vary wonderfully little, considering the nature 

 of the structure investigated and the difficulties connected with the method. 



The experiment just alluded to also indicates a very important feet which will be 

 referred to in detail in the concluding section of this work, namely, that when the 

 stimulus is minima] the nerve impulses are almost entirely confined to the direct 

 path ; in other words, this path is that of least resistance. It is necessary for the 

 stimulus to be of a certain intensity before nerve impulses can be started of sufficient 

 volume to break through corpuscular structures and so enter on indirect paths. This 

 is indicated by the feet that no change in the deflection could be observed in the case 

 of the weak initial stimulus to follow the section of the grey matter ; presumably, 

 therefore, the cord effect was due, in this case, to afferent impulses passing up the 

 .-. 



A further extension of the experiment just described may be now referred to, 

 namely, the in&amp;lt;iiu&amp;lt;* of dividing in addition one posterior column. After the section 

 of the anterior or ventral portion of the cord the left posterior column was divided at 

 the 10th dorsal vertebra ; on now stimulating the left sciatic nerve an effect of 8 only 

 was obtained, this observation being repeated several times. The importance of the 

 posterior column on the side of the nerve is thus forcibly brought into view. 



