ON THE MAMMALIAN NERVOUS SYSTEM. 321 



taken to be an indication of the amount of potential energy, which the nerve material 

 is capable of making kinetic in the form of a nerve impulse, then this remarkable 

 rise, and the conditions which determine it, would appear to show that the physio- 

 logical characters of the structure upon which the storage of energy depends, are such 

 as to be rendered more efficacious with use, and that the central structures (cells) of 

 the cord play the most prominent part in this influence of functional use upon 

 efficiency. 



CHAPTER V. ON THE ELECTRICAL EFFECTS EVOKED IN THE SPINAL CORD AND 

 MIXED NERVES BY EXCITATION OF THE CORTEX CEREBRI. 



The primary object of this work being the determination of the nature of the 

 impulses which issue from the excitable or so-called motor cortex, considerable 

 importance attaches to positive results on this point. As, however, usually happens 

 in the employment of a new method, we have found that more actual advance was 

 made by applying it to the study of the lower centres and fibres through which these 

 impulses pass than by attempting to elucidate the functional relations existing 

 between one part of the cortex and the rest of the encephalon. 



One fundamental fact stands out, however, prominently, viz., that, as we shall see 

 directly, it is possible to ascertain and judge the nature and comparative amount of 

 the electrical changes which accompany the descent of the cortical impulses in the 

 spinal cord, and so to learn the character of the cortical discharge. Practically, there- 

 fore, the results of our special investigation of the excited cortex will best be 

 arranged according to the part of the nervous system in which the electrical changes 

 were observed. A further subdivision of such a classification will be necessary in 

 order to bring out the wider points of interest which have received elucidation by the 

 use of this method, and this is furnished by the summary and arrangement we have 

 given on pp. 272-276, of the facts discovered by other methods, of which the most 

 notable are those of simple inspection and of graphic record respectively. 



In accordance with this plan, therefore, we will commence with considering the 

 case in which we observed the electrical changes in the dorsal cord, with the object 

 of ascertaining the character of the descending nervous impulses in consequence of 

 stimulation of the cortex. 



We have employed in these experiments on the relations of the cortex cerebri to 

 the bulbo-spinal and peripheral systems fifteen Monkeys and thirty-two Cats. 



MDCCOXCI.-B. 2 T 



