494 MESSRS. F. GOTCH AND V. HORSLEY 



elicited by the one or the other of these two ways. We, therefore, separate the effects 

 into two divisions indicating this difference. 



Posterior Root. The general results in this series of experiments were as follows : 



EFFECTS in nerve by excitation of opposite root. 



Highest readings 45 42 42 (three highest taken). 



Average 25 



Lowest readings 8 6 nil (three lowest taken). 



These figures are, on the whole, lower than those of the simple reflex. Other 

 considerations emphasise this contrast. These are (1) the proportionate number of 

 cases in which no effect occurred, this being, with the simple reflex, 9 per cent, 

 of the total number of observations, but with the crossed reflex. three times as much, 

 viz., 27 per cent. ; (2) the average intensity of the stimulus required to evoke the 

 effect, this being for a simple reflex, an intensity indicated by the secondary coil at 

 2500, for the crossed reflex the higher intensity indicated by the coil at 3500. Thus, 

 as compared with the simple reflex, the crossed reflex is feebler, less often obtained, 

 and when obtainable requiring a more pronounced stimulus applied to the afferent 

 fibres in a posterior root. 



Sciatic Nerve. In addition to the above we have observed crossed reflex effects 

 which are not comparable with the simple uncrossed effects, since they were evoked 

 by excitation, not of a root, but of the opposite sciatic nerve. 



These effects are smaller and more difficult to elicit than those just indicated. 



The effects were evoked and observed in precisely the same manner as in the 

 previous cases, and the amounts of the deflections in the central end of the sciatic 

 nerve were as follows : 



Highest readings 20 15 14 (three highest taken). 



Average 10 



Lowest readings 6 5 



The intensity of stimulus required to evoke these effects was very much higher 

 than in either of the previous instances, the average being represented by a position 

 of the secondary coil of 8300, whilst it often happened that a position of 12,000 was 

 necessary. It may be remarked that the use of the Helmholtz side-wire in the induc- 

 torium minimised any error due to electrotonic escape, such as produces the well-known 

 phenomenon of the so-called " paradoxical contraction." 



We are now in a position to consider the significance of these results. 



The remarkable dift'erence in quantity between the electrical effect in the nerve 

 obtained by exciting the fibres themselves and that which is the result of a reflex 

 discharge from the cord implies that, however intense the excitation of the afferent 



