ON THE MAMMALIAN NERVOUS SYSTEM. 355 



The method under consideration, with both cortices exposed but intact, is not, 

 however, favourable for testing bilaterality, since we have often had occasion to 

 observe the great inequality in the excitability of the two hemispheres, which appears 

 to be to a large extent connected with the necessary exposure of one cortex before 

 the other. 



From the result of other experiments we are inclined to believe that the effects 

 (average 32) observed in the half of the cord on the side of the cortical excitation is 

 due to the passage of impulses which have descended from the cortex opposite to that 

 directly stimulated, but several interpretations are, of course, possible. In this con- 

 nection it must be remembered that we do not yet know whether a direct pyramidal 

 tract exists in the Carnivora (most authors denying its presence), and, further, that 

 possibly even the galvanometer may not show an excitatory disturbance if the fibres 

 by which the hemisphere of one side might be in relation with the same side of the 

 spinal cord were very few in number. 



II. Excitation of Cortex. Effect in Cord after previous Hemisection. 



The next step was to ascertain the effect of a previously performed hemisection of 

 the cord between the encephalon and the observed region, the experiment being made 

 with the view of eliminating any presumably crossed discharge from the cortex 

 opposite to that excited. 



The following experiment was made : In a Cat (225) the right half of the cord was 

 divided under antiseptic precautions at the level of the lower border of the 9th dorsal 

 vertebra. In this case there was well-marked motor paralysis in the right hind limb 

 with rigidity, and diminution of perception of sensory stimulation of the same limb. 

 The right knee jerk was exaggerated. When partly etherised the right hind limb 

 became flaccid and the left somewhat rigid, the knee jerk then on the right side was 

 greatly exaggerated and marked clonus present. These facts were noted just before 

 the experiment now to be described. Eighty-four days later the cord was exposed 

 and divided below the lesion, and the central end of the whole cord connected with 

 the galvanometer electrodes. (See fig. 9.) The two cortices were then exposed and 

 excited with an intensity of stimulus indicated by coil 8000 for 5 seconds. 



The following definite results were obtained : 



In the first place excitation of each hemisphere evidently produced unilateral 

 epileptic fits. The effect in the descending (lower limb) fibres of the cord was as 

 follows, it being remembered that the right half of the spinal cord had been divided. 

 Excitation of the right cortex which produced unilateral fits on the left side of the 

 body, gave a variation of 82 degrees in the galvanometer, whereas excitation of the 

 left cortex, although it produced a good unilateral fit in the parts above the section, 

 i.e., right upper limb, gave nothing in the galvanometer, although the whole cord 



ablation of one hemisphere or excitable area in Cats, that apparently in that animal complete unilaterality 

 of tho true cortical discharge (i.e., tonus plus clonus) existed. 



2 z 2 



