330 HESS US. P. GOTCH AND V. HORSLEY 



where, according to BEEVOR and one of us, the upper and lower limb areas tend to 

 overlap, with the same stimulus as in the latter case this region was the last from which 

 any effect could be produced in the fibres of the dorsal cord. Even in the case where 

 the whole cortex was very excitable, and where a generalised effect was thus easily 

 evoked, and where, consequently, electrical effects in the cord followed stimulation of 

 the upper third of the upper limb area, the general effect was, nevertheless, most 

 markedly graduated from the centre of the lower limb area in diminishing order as 

 the electrodes were removed downwards and passed the level of the superior frontal 

 sulcus. 



We may now allude to the obvious inference that might be drawn from these 

 experiments, namely, that although there is no sharply marked line of demarcation 

 between the cortical foci, there is nevertheless in the facts we have just stated a 

 certain amount of evidence against the assumption that the lower limb, for example, is 

 represented to any marked degree in the upper limb area of the cortex. We do not 

 speak with great positiveness on this point, because it may well be that the instru- 

 ment we chiefly used in this branch of our work, the electrometer, was not sufficiently 

 delicate to show the extremely minute variation which might be supposed to result 

 from the excitation of only a very few fibres. That this indeed seems probable is 

 shown by the results of two experiments which we performed with the galvanometer 

 instead of the electrometer. Unfortunately, however, they do not enable us to speak 

 with greater certainty in the directions indicated, because in each instance the cortex 

 was hyperexcitable from the commencement of the experiment. This, however, is 

 clearly a branch of enquiry which might with advantage be followed out by subsequent 

 observers. 



In this connection the experiments of SHEEEINGTON* are very suggestive, and we 

 shall refer again to this part of the subject in describing our experiments on bilateral 

 representation. 



(d.) The Amount of the Galvanometric Readings. 



Although, as has been stated, no exact comparison for quantitative purposes can 

 be made between different deflections of the galvanometer, when, being connected 

 with the central end of the exposed spinal cord, the cortex is excited, yet the 

 amounts of the different readings are in themselves of great interest, owing to the fact 

 that it is always possible with an excitable cortex and a sufficiently strong excitation 

 to obtain very large galvanometric deflections. It is obvious that the deflection is 

 dependent not merely upon the intensity but the duration of the stimulation, hence 

 the excitation was limited by the revolving key, previously described, to 5 seconds. 

 Since, however, the cortical discharge lasts a variable time after the stimulus has ceased, 



* ' Proceedings of the Physiological Society,' 1890. 



