352 MESSRS. F. GOTCH AND V. HORSLEY 



As regards the method of observation, the electrical changes in each half of the longitu- 

 dinally divided cord were recorded by means of the galvanometer, since it was essential 

 to obtain results which admitted of relatively strict comparison as to their amounts. 

 Each half of the cord was therefore attached to an independent pair of nori-polaris- 

 able electrodes, and an arrangement made by which either pair could at any desired 

 moment be switched into connection with the wires leading to the galvanometer, &c. 



The result of this experimental investigation may be divided into groups, each one 

 of which we must consider in detail. 



I. Excitation of Cortex (whole Encephalon intact). Electrical Changes in each 



half of Longitudinally Divided Cord. 



The cord having been divided, and split as just indicated, one cortical surface 

 was exposed and the animal having been brought as far as possible into a perfectly 

 steady, i.e., constant state of narcotisation, the same strength of stimulus was then 

 applied to the cortex, first one half of the cord being in connection with the galvano- 

 meter, and then the opposite half (see fig. 8). The results obtained, i.e., from the 

 opposite side of the spinal cord, and from the same side respectively, were then 

 gathered together and averages taken. 



It will be best to begin with the results of special experiments. Of these, the 

 first we will refer to were made upon an animal (Cat 237), in which, from the move- 

 ments of the upper limb, it was very easy to ascertain when the muscular contractions 

 were unilateral or bilateral. It was seen that when the said contractions were strictly 

 unilateral, the excitation of the hemisphere produced no result in the half of the cord 

 on the same side, but a marked result in the half of the cord of the opposite side, viz., 

 275 degrees of the scale. 



In this case complete unilaterality for the lower limb existed as far as the pyramidal 

 tracts in the cord were concerned, for the cortex was, as we have before indicated in 

 the first of our considerations, completely discharged, the discharge being evidenced 

 by the large effect in the corresponding half of the cord, yet no electrical change 

 could be seen in the other half indicative of descending impulses. 



In another experiment made upon a Monkey (21 5), both cortices were exposed for 

 excitation. In this animal, it was easy to confine the excitation apparently to one 

 hemisphere, although, judging from the contractions of the muscles of the upper limb, 

 the cortex excited was very completely discharged. In this instance, the cord was 

 divided as described between the 10th and llth dorsal nerves; the resting electrical 

 difference of the two halves wa.s in the proportion of two to one, the smaller being 

 the right. 



For the convenience of brevity, we will speak of the halves of the cord as the " right 

 cord " and " left cord " respectively. 



Excitation of the left hemisphere gave, with the coil at 5000, an effect in the right 

 half of the cord of 425 degrees, and then, the right cord still remaining in connection 



