ON THE MAMMALIAN NERVOUS SYSTEM. 



367 



excitation and commencement of muscular response, when the former occurred at the 

 level of the 5th cervical and 2nd lumbar nerves respectively : 



CAT (163). 



The distance between the 5th cervical and the 2nd lumbar was found to be 

 17 centims., and since the average difference of time between the muscular response 

 evoked by the excitation at the two regions is '0043, this difference indicates that the 

 cord delay is such as would be caused if the nerve impulses starting from the cervical 

 region travelled along the cord at 39^ metres per second. This experiment, therefore, 

 seems to show that the time occupied by the conduction of nerve impulses in the 

 Mammalian cord closely resembles that occupied by their conduction in nerve trunks ; 

 and it confirms the view that there is an efferent path in the cord leading from the 

 cervical to the lumbar region in which a physiological continuity exists similar to that 

 which forms the basis of nerve conduction in the fibres of mixed nerve trunks. 



It will be noticed that the more exact physiological methods just referred to rely upon 

 the observation of muscular movements. This involves serious disadvantages, since, 

 in the first place, the method is thereby limited to the efferent fibres, and thus the 

 physiological scope of any inquiry is narrowed ; whilst, in the second place, the struc- 

 tural connections between the efferent fibres in the cord and the anterior roots of the 

 nerves is to a great extent unknown, and certainly involves cellular elements, thus 

 introducing new physiological conditions. 



There is, as it seems to us, only one line of experimental enquiry which is free from 

 these objections that, namely, of ascertaining the existence of the nerve impulses in 

 the fibres of the spinal cord itself, through careful quantitative observations of the 

 electrical effects by which they are accompanied. 



The present chapter will be devoted to the consideration in detail of the results of 

 such observations in the dorsal and lumbar regions of the cord respectively. The 

 novelty of the method, and the important bearing which the results have upon the 

 physiology of the cord, we trust will warrant this extended treatment. 



