382 



MESSRS. F. GOTCF AND V. HORSLEY 



A further result which an analysis of these effects shows, is the difference between 

 the average deflection in the case of the posterior and the lateral column with weak 

 minimal stimulation and maximal stimulation respectively. 



AVERAGE effect evoked by stimulation of one lateral column. 



AVERAGE effect evoked by stimulation of one posterior column. 



It is seen that in the Cat both minimal and maximal stimulation evoke effects 

 which are twice as large in the case of the posterior columns as in that of the 

 laterals. 



In the Monkey the lateral column effect with minimal stimulation is, on the other 

 hand, twice as large as that produced by the stimulation of the posterior column, but 

 with a stronger stimulus this relationship does not hold, owing, possibly, to the 

 increased reflex discharge which excitation of the posterior column now evokes. 



The difference between the results of excitation of the columns in the two animals 

 is, therefore, best marked with the weaker intensity of stimulus. It is evident that 

 this must depend upon the number of fibres which form direct connections between the 

 excited dorsal and observed lumbar region, along which fibres as constituting paths of 

 least resistance the nerve impulses are almost entirely propagated from the excited 

 area, when the fibres this contains are aroused by a weak stimulus. 



This seems to us to afford an experimental proof of the relatively larger number 

 of continuous lateral column-fibres which must exist in the Monkey as compared 

 with the Cat ; this greater proportion may, in the light of the previous results 

 described under cortical stimulation (Chapter V.), be ascribed to the more complete 

 development of the fibres forming the pyramidal tracts. 



The histological investigation of the fibres in the tract in the two animals seems to 

 support this view, there being apparently many more fibres in the pyramidal tract of 

 the Monkey than in that of the Dog, as determined by the degeneration method. It 

 is, moreover, to be expected that the fibres in question must increase in number 

 with the completeness of the differentiation of those cortical structures from which 



