On the relative length of the period of latency of the ocular muscles etc. 151 



Two pairs of flat platinum wire electrodes, carefully guarded with 

 paraffin, were applied through trephine openings, the one to the motor 

 area for the head and eyes in the frontal region, and the other to a 

 sensory area (either the superior temporal convolution, or the surface 

 of the occipital lobe) The wires from these two pairs of electrodes 

 passed to a switch by means of which the induced currents from a 

 Du Bois coil (having a Helmholtz side- wire in the primary circuit) 

 could be directed alternately to either the frontal (motor) or to one 

 of the posterior (sensory) regions. The lateral movement of one of 

 the eyes was recorded by attaching to the sclerotic a very fine sharp 

 steel hook, from which a thread was carried to the short arm of a 

 light bell-crank lever writing upon a blackened surface of glazed paper 

 stretched over a cylinder which was kept revolving at a perfectly uni- 

 form rate by clockwork. The apparatus was arranged so that both the 

 moment of commencement, and the duration of the excitation were 

 marked by causing the lever itself to transmit sparks from a Ruhm- 

 korff coil to the drum, and thus to mark the blackened paper with a 

 series of dots corresponding to the rate of interruption of the current 

 working the Ruhmkorff. The period of latency for each excitation was 

 measured from the commencement of these sparks (in each case) to 

 the commencement of rise of the lever, and in all the experiments 

 a series of excitations was applied alternately to the frontal and pos- 

 terior area, with intervals only long enough to allow the lever to come 

 back to the position of rest. In this way a number of dotted (spark) 

 tracings of the eye -movement were obtained upon the paper, produced 

 alternately by excitation of frontal and occipital regions in some expe- 

 riments, or of frontal and temporal in others, or again in one or two experi- 

 ments by alternate excitation of occipital and temporal regions. By 

 alternating the excitations in this way certain errors which would tend 

 to mar the attainment of the desired result, viz : the institution of 

 an accurate comparison between the results of the excitation of the 

 two regions, are in great measure obviated. These errors would be 

 caused by the varying irritability of the cortex from exposure, or from 

 a different degree of ether -anaesthesia, and they are minimized by the 

 adoption of this plan of rapidly alternating the excitations. 



A diagram showing the method of conducting an experiment is 



